Biomonitoring: Phthalates
Methods
Indicator
Indicator B9: Phthalate metabolites in women ages 16 to 49 years: Median concentrations in
urine, 1999-2016
Indicator BIO: Phthalate metabolites in children ages 6 to 17 years: Median concentrations in
urine, 1999-2016
Summary
Since the 1970s, the National Center for Health Statistics, a division of the Centers for Disease
Control and Prevention, has conducted the National Health and Nutrition Examination Surveys
(NHANES), a series of U.S. national surveys of the health and nutrition status of the non-
institutionalized civilian population. The National Center for Environmental Health at CDC
measures environmental chemicals in blood and urine samples collected from NHANES
participants.1 This indicator uses urine measurements of three phthalate metabolites in women
ages 16 to 49 years and children ages 6 to 17 years. The three phthalate metabolites analyzed are:
DBP metabolites: the sum of the two metabolites mono-n-butyl phthalate (MBP) and mono-
isobutyl phthalate (MIB); BBzP metabolite: mono-benzyl phthalate (MBzP); and DEHP
metabolites: the sum of the three metabolites mono-2-ethylhexyl phthalate (MEHP), mono-(2-
ethyl-5-oxohexyl) phthalate (MEOHP), and mono-(2-ethyl-5-hydroxyhexyl) phthalate
(MEHHP). The two isomers mono-n-butyl phthalate (MBP) and mono-isobutyl phthalate (MIB)
were measured together as a total in the NHANES 1999-2000 survey but were measured
separately in the NHANES 2001-2016 surveys. The NHANES 1999-2016 surveys included urine
phthalate metabolite data for these three metabolites for children ages 6 to 17 and adults ages 16
to 49 years, except that MEOHP and MEHHP were not measured in 1999-2000.
Indicator B9 is the trend in the median concentrations of the phthalate metabolites for women
ages 16 to 49 years for 1999-2016. The median is the estimated concentration such that 50% of
all non-institutionalized civilian women ages 16 to 49 years have a phthalate metabolite
concentration below this level; the population distribution was adjusted by age-specific birth
rates to estimate the median prenatal exposure to phthalate metabolites.
Supplementary Tables: Table B9a presents the 95th percentile concentrations of phthalate
metabolites for women ages 16 to 49 years for 1999-2016. The 95th percentile for women is the
estimated concentration such that 95% of all non-institutionalized civilian women ages 16 to 49
years have a phthalate metabolite concentration below this level. Table B9b presents the median
concentration of phthalate metabolites for women ages 16 to 49 in 2013-2016, stratified both by
race/ethnicity and family income. Indicator B10 is the trend in the median concentrations of the
1 Centers for Disease Control and Prevention. 2009. Fourth National Report on Human Exposure to Environmental
Chemicals. Atlanta, GA. Available at: www.cdc.gov/exposurereport.
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Biomonitoring: Phthalates
phthalate metabolites for children ages 6 to 17 years for 1999-2016. Table BlOa presents the
trend in the 95th percentile concentration of phthalate metabolites for children ages 6 to 17 in
1999-2016. Table B 10b presents the median concentration of phthalate metabolites for children
ages 6 to 17 years in 2013-2016, stratified both by race/ethnicity and family income. Table BlOc
presents the median concentration of phthalate metabolites for children ages 6 to 17 in 2013-
2016, stratified by age group. The survey data were weighted to account for over-sampling, non-
response, and non-coverage.
Data Summary
Indicator B9: Phthalate metabolites in women ages 16 to 49 years: Median concentrations in
urine, 1999-2016
Data
Urine phthalate meta
jolites in women
ages 16 to 49
Years
1999-
2000
2001-
2002
2003-
2004
2005-
2006
2007-
2008
2009-
2010
2011-
2012
2013-
2014
2015-
2016
Limits of Detection
(ng/mL)*
0.9
1.1
0.4
0.6
0.6
0.4
0.4
0.4
0.4
CLh
Number of Values
642
688
626
634
589
618
542
612
585
CO
5
Number of Non-Missing
Values**
618
(96%)
659
(96%)
606
(97%)
616
(97%)
571
(97%)
608
(98%)
536
(99%)
599
(98%)
564
(96%)
Number of Missing
Values**
24
(4%)
29
(4%)
20
(3%)
18
(3%)
18
(3%)
10
(2%)
6
(1%)
13
(2%)
21
(4%)
Percentage Below Limit
of Detection* * *
2
2
1
1
1
1
9
4
1
Years
1999-
2000
2001-
2002
2003-
2004
2005-
2006
2007-
2008
2009-
2010
2011-
2012
2013-
2014
2015-
2016
Limits of Detection
(ng/mL)*
No
data
1.0
0.26
0.3
0.3
0.2
0.2
0.8
0.8
MIB
Number of Values
0
688
626
634
589
618
542
612
585
Number of Non-Missing
Values**
0
659
(96%)
606
(97%)
616
(97%)
571
(97%)
608
(98%)
536
(99%)
599
(98%)
564
(96%)
Number of Missing
Values**
0
29
(4%)
20
(3%)
18
(3%)
18
(3%)
10
(2%)
6
(1%)
13
(2%)
21
(4%)
Percentage Below Limit
of Detection* * *
No
data
23
2
4
2
0.4
1
4
2
Years
1999-
2000
2001-
2002
2003-
2004
2005-
2006
2007-
2008
2009-
2010
2011-
2012
2013-
2014
2015-
2016
Limits of Detection
(ng/mL)*
0.58
0.22
0.07
0.22
0.22
0.22
0.3
0.3
0.3
a.
Number of Values
642
688
626
634
589
618
542
612
585
CO
5
Number of Non-
Missing Values**
618
(96%)
659
(96%)
606
(97%)
616
(97%)
571
(97%)
608
(98%)
536
(99%)
599
(98%)
564
(96%)
Number of Missing
Values**
24
(4%)
29
(4%)
20
(3%)
18
(3%)
18
(3%)
10
(2%)
6
(1%)
13
(2%)
21
(4%)
Percentage Below
Limit of Detection* * *
1
1
0
2
3
1
2
2
3
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Biomonitoring: Phthalates
Data
Urine phthalate meta
jolites in women ages 16 to 49
MEHP
Years
1999-
2000
2001-
2002
2003-
2004
2005-
2006
2007-
2008
2009-
2010
2011-
2012
2013-
2014
2015-
2016
Limits of Detection
(ng/mL)*
1.2
1.0
0.9
1.2
1.1
0.5
0.5
0.8
0.8
Number of Values
642
688
626
634
589
618
542
612
585
Number of Non-
Missing Values**
618
(96%)
659
(96%)
606
(97%)
616
(97%)
571
(97%)
608
(98%)
536
(99%)
599
(98%)
564
(96%)
Number of Missing
Values**
24
(4%)
29
(4%)
20
(3%)
18
(3%)
18
(3%)
10
(2%)
6
(1%)
13
(2%)
21
(4%)
Percentage Below
Limit of Detection* * *
21
19
23
27
25
22
25
38
35
MEOHP
Years
1999-
2000
2001-
2002
2003-
2004
2005-
2006
2007-
2008
2009-
2010
2011-
2012
2013-
2014
2015-
2016
Limits of Detection
(ng/mL)*
No
data
1.1
0.45
0.7
0.6
0.2
0.2
0.2
0.2
Number of Values
0
688
626
634
589
618
542
612
585
Number of Non-
Missing Values**
0
659
(96%)
606
(97%)
616
(97%)
571
(97%)
608
(98%)
536
(99%)
599
(98%)
564
(96%)
Number of Missing
Values
0
29
(4%)
20
(3%)
18
(3%)
18
(3%)
10
(2%)
6
(1%)
13
(2%)
21
(4%)
Percentage Below
Limit of Detection* * *
No
data
6
0.4
1
1
0
1
1
0.4
MEHHP
Years
1999-
2000
2001-
2002
2003-
2004
2005-
2006
2007-
2008
2009-
2010
2011-
2012
2013-
2014
2015-
2016
Limits of Detection
(ng/mL)*
No
data
1.0
0.32
0.7
0.7
0.2
0.2
0.4
0.4
Number of Values
642
688
626
634
589
618
542
612
585
Number of Non-
Missing Values**
0
659
(96%)
606
(97%)
616
(97%)
571
(97%)
608
(98%)
536
(99%)
599
(98%)
564
(96%)
Number of Missing
Values**
0
29
(4%)
20
(3%)
18
(3%)
18
(3%)
10
(2%)
6
(1%)
13
(2%)
21
(4%)
Percentage Below
Limit of Detection* * *
No
data
3
0.2
0.1
1
0
0.1
0.4
0
* The Limit of Detection (LOD) is defined as the level at which the measurement has a 95% probability of being greater than
zero.
**Non-missing values include those below the analytical LOD, which are reported as LOD/V2. Missing values are the number of
sampled women ages 16 to 49 years in the Mobile Examination Center (MEC) sub-sample that have no value reported for the
particular variable used in calculating the indicator.
"This percentage is survey-weighted using the NHANES MEC survey weights for the given period and is weighted by age-
specific birth rates.
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April, 2022
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Biomonitoring: Phthalates
Indicator BIO. Phthalate metabolites in children ages 6 to 17 years: Median concentrations in
urine, 1999-2016
Data
Urine phthalate meta
jolites in children ages 6 to 17
Years
1999-
2001-
2003-
2005-
2007-
2009-
2011-
2013-
2015-
2000
2002
2004
2006
2008
2010
2012
2014
2016
Limits of
Detection
0.9
1.1
0.4
0.6
0.6
0.4
0.4
0.4
0.4
(ng/mL)*
Number of
Values
940
1005
931
927
714
743
706
789
789
MBP
Number of Non-
900
960
895
896
690
727
689
750
742
missing
Values**
(96%)
(96%)
(96%)
(97%)
(97%)
(98%)
(98%)
(95%)
(94%)
Number of
Missing
Values**
40
(4%)
45
(4%)
36
(4%)
31
(3%)
24
(3%)
16
(2%)
17
(2%)
39
(5%)
47
(6%)
Percentage
Below Limit of
0.1
1
0
0.3
0.3
0.4
4
1
1
Detection* * *
Years
1999-
2001-
2003-
2005-
2007-
2009-
2011-
2013-
2015-
2000
2002
2004
2006
2008
2010
2012
2014
2016
Limits of
No
data
Detection
1.0
0.26
0.3
0.3
0.2
0.2
0.8
0.8
(ng/mL)*
Number of
Values
0
1005
931
927
714
743
706
789
789
CO
Number of
Non-missing
Values**
0
960
895
896
690
727
689
750
742
5
(96%)
(96%)
(97%)
(97%)
(98%)
(98%)
(95%)
(94%)
Number of
Missing
Values**
0
45
(4%)
36
(4%)
31
(3%)
24
(3%)
16
(2%)
17
(2%)
39
(5%)
47
(6%)
Percentage
Below Limit
No
17
1
1
1
0
1
9
1
of
data
z,
Detection* * *
Years
1999-
2001-
2003-
2005-
2007-
2009-
2011-
2013-
2015-
2000
2002
2004
2006
2008
2010
2012
2014
2016
Limits of
Detection
0.58
0.22
0.07
0.22
0.22
0.22
0.3
0.3
0.3
(ng/mL)*
a.
N
CO
Number of
Values
940
1005
931
927
714
743
706
789
789
Number of
Non-missing
Values**
900
960
895
896
690
727
689
750
742
(96%)
(96%)
(96%)
(97%)
(97%)
(98%)
(98%)
(95%)
(94%)
Number of
Missing
Values**
40
(4%)
45
(4%)
36
(4%)
31
(3%)
24
(3%)
16
(2%)
17
(2%)
39
(5%)
47
(6%)
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Biomonitoring: Phthalates
Data
Urine phthalate meta
jolites in children ages 6 to 17
Percentage
Below Limit
of
1
0
0
1
1
0.1
1
1
2
Detection* * *
Years
1999-
2001-
2003-
2005-
2007-
2009-
2011-
2013-
2015-
2000
2002
2004
2006
2008
2010
2012
2014
2016
Limits of
Detection
1.2
1.0
0.9
1.2
1.1
0.5
0.5
0.8
0.8
(ng/mL)*
Number of
Values
940
1005
931
927
714
743
706
789
789
CLh
X
Number of
Non-missing
Values**
900
960
895
896
690
727
689
750
742
W
5
(96%)
(96%)
(96%)
(97%)
(97%)
(98%)
(98%)
(95%)
(94%)
Number of
Missing
Values**
40
(4%)
45
(4%)
36
(4%)
31
(3%)
24
(3%)
16
(2%)
17
(2%)
39
(5%)
47
(6%)
Percentage
Below Limit
of
15
16
26
26
31
19
21
36
35
Detection* * *
Years
1999-
2001-
2003-
2005-
2007-
2009-
2011-
2013-
2015-
2000
2002
2004
2006
2008
2010
2012
2014
2016
Limits of
No
data
Detection
1.1
0.45
0.7
0.6
0.2
0.2
0.2
0.2
(ng/mL)*
Number of
Values
0
1005
931
927
714
743
706
789
789
V1EOHP
Number of
Non-missing
Values**
0
960
(96%)
895
(96%)
896
(97%)
690
(97%)
727
(98%)
689
(98%)
750
(95%)
742
(94%)
Number of
Missing
Values**
0
45
(4%)
36
(4%)
31
(3%)
24
(3%)
16
(2%)
17
(2%)
39
(5%)
47
(6%)
Percentage
Below Limit
No
1
0
0
1
0.2
1
0.1
1
of
data
Detection* * *
Years
1999-
2001-
2003-
2005-
2007-
2009-
2011-
2013-
2015-
2000
2002
2004
2006
2008
2010
2012
2014
2016
Limits of
No
data
a.
Detection
1.0
0.32
0.7
0.7
0.2
0.2
0.4
0.4
X
X
w
s
(ng/mL)*
Number of
Values
0
1005
931
927
714
743
706
789
789
Number of
Non-missing
Values**
0
960
895
896
690
727
689
750
742
(96%)
(96%)
(97%)
(97%)
(98%)
(98%)
(95%)
(94%)
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Biomonitoring: Phthalates
Data
Urine phthalate meta
jolites in children ages 6 to 17
Number of
Missing
Values**
0
45
(4%)
36
(4%)
31
(3%)
24
(3%)
16
(2%)
17
(2%)
39
(5%)
47
(6%)
Percentage
Below Limit
No
1
0.2
0.1
0.2
0.1
0
1
1
of
data
Detection* * *
* The Limit of Detection (LOD) is defined as the level at which the measurement has a 95% probability of being greater than
zero.
**Non-missing values include those below the analytical LOD, which are reported as LOD/V2. Missing values are the number of
sampled children ages 6 to 17 years in the Mobile Examination Center (MEC) sub-sample that have no value reported for the
particular variable used in calculating the indicator.
"This percentage is survey-weighted using the NHANES MEC survey weights for the given period.
National Health and Nutrition Examination Surveys (NHANES)
Since the 1970s, the National Center for Health Statistics, a division of the Centers for Disease
Control and Prevention, has conducted the National Health and Nutrition Examination Surveys
(NHANES), a series of U.S. national surveys of the health and nutrition status of the non-
institutionalized civilian population. The National Center for Environmental Health at CDC
measures environmental chemicals in blood and urine samples collected from NHANES
participants.
This indicator uses urine phthalate metabolite concentrations for the six metabolites listed in the
following table from NHANES 1999-2000, 2001-2002, 2003-2004, 2005-2006, 2007-2008,
2009-2010, 2011-2012, and 2013-2014 in women ages 16 to 49 and children ages 6 to 17. The
NHANES data were obtained from the NHANES website: http://www.cdc.gov/nchs/nhanes.htm.
Following the CDC recommended approach, values below the analytical limit of detection
(LOD) were replaced by LOD/V2."
Phthalate metabolite
Full name
SAS® name
SAS® name for non-
detect comment code*
MBP
mono-n-butyl phthalate
URXMBP
URDMBPLC
MIB
mono-isobutyl
phthalate
URXMIB
URDMIBLC
MBzP
mono-benzyl phthalate
URXMZP
URDMZPLC
MEHP
mono-2-ethylhexyl
phthalate
URXMHP
URDMHPLC
MEOHP
mono-(2-ethyl-5-
oxohexyl) phthalate
URXMOH
URDMOHLC
MEHHP
mono-(2-ethyl-5-
hydroxyhexyl)
phthalate
URXMHH
URDMHHLC
11 See Hornung RW, Reed LD. 1990. Estimation of average concentration in the presence of nondetectable values.
Applied Occupational and Environmental Hygiene 5:46-51.
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Biomonitoring: Phthalates
*The non-detect comment code equals 1 if the measurement is below the analytical limit of detection and equals 0 if the
measurement is at or above the analytical limit of detection. The non-detect comment code variables were not included in
NHANES 1999-2000 and 2001-2002.
The analytes studied are the sum of MBP and MIB, MBzP, and the sum of MEHP, MEOHP, and
MEHHP. In NHANES 1999-2000, MBP and MIR were measured together as a total and
reported as MBP. In NHANES 1999-2000, MEOHP and MEHHP were not measured and the
sum of MEHP, MEOHP, and MEHHP is missing. In NHANES 2001-2016 every sample
measurement either had both of MBP and MIB, or neither of these phthalate metabolites. In
NHANES 2001-2016, every sample measurement either had all three of MEHP, MEOHP, and
MEHHP, or none of these phthalate metabolites. For the sum of MBP and MIB, and the sum of
MEHP, MEOHP, and MEHHP, the sums are treated as being non-detects if one or more of the
constituent phthalate metabolites is a non-detect. For calculating the sums, any constituent
phthalate metabolite that is below its analytical limit of detection (LOD) is replaced by LOD/V2
before adding the concentrations.
The NHANES use a complex multi-stage, stratified, clustered sampling design. Certain
demographic groups were deliberately over-sampled, including Mexican-Americans, Blacks,
and, from 2007 onwards, All Hispanics, to increase the reliability and precision of estimates of
health status indicators for these population subgroups. The publicly released data includes
survey weights to adjust for the over-sampling, non-response, and non-coverage. The statistical
analyses used the applicable MEC sub-sample survey weights (WTSPH2YR for 1999-2002,
WTSB2YR for 2003-2010 and 2013-2016, and WTSA2YR for 2011-2012) to re-adjust the urine
phthalate metabolite data to represent the national population.
Age-Specific Birth Rates
In addition to the NHANES MEC survey weights, the data for women ages 16 to 49 were also
weighted by the birth rate for women of the given age and race/ethnicity to estimate prenatal
exposures. Thus, the overall weight in each two-year period is the product of the NHANES
survey weight and the total number of births in the two calendar years for the given age and
race/ethnicity, divided by twice the corresponding population of women at the midpoint of the
two-year period:111
Adjusted Survey Weight =
MEC survey weight x U.S. Births (NHANES cycle, age, race/ethnicity) /
{Number of years in NHANES cycle x U.S. Women (NHANES cycle midpoint, age,
race/ethnicity)}.
Race/Ethnicity and Family Income
For this indicator, the percentiles were calculated for demographic strata defined by the
combination of race/ethnicity and family income.
mAxelrad, D.A., Cohen, J. 2011. Calculating summary statistics for population chemical biomonitoring in women of
child-bearing age with adjustment for age-specific natality. Environmental Research 111 (1): 149-155.
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Biomonitoring: Phthalates
The family income was characterized based on the INDFMPIR variable, which is the ratio of the
family income to the poverty level. The National Center for Health Statistics used the U.S.
Census Bureau Current Population Survey definition of a "family" as "a group of two people or
more (one of whom is the householder) related by birth, marriage, or adoption and residing
together" to group household members into family units, and the corresponding family income
for the respondent was obtained during the interview. The U.S. Census Bureau defines annual
poverty level money thresholds varying by family size and composition. The poverty income
ratio (PIR) is the family income divided by the poverty level for that family. Family income was
stratified into the following groups:
• Below Poverty Level: PIR < 1
• Above Poverty Level: PIR > 1
• Unknown Income: PIR is missing
For the four-year period 2013-2016, the weighted percentage of women ages 16 to 49 years with
unknown income was 7% and the weighted percentage of children ages 6 to 17 years with
unknown income was 6%.
Race/ethnicity was characterized using the RIDRETH1 variable. The possible values of this
variable are:
• 1. Mexican American
• 2. Other Hispanic
• 3. Non-Hispanic White
• 4. Non-Hispanic Black
• 5. Other Race - Including Multi-racial
• "." Missing
Category 5 includes: all Non-Hispanic single race responses other than White or Black; and
multi-racial responses.
For this indicator, the RIDRETH1 categories 2, 5, and missing were combined into a single "All
Other Races/Ethnicities" category. This produced the following categories:
• White non-Hispanic: RIDRETH1 = 3
• Black non-Hispanic: RIDRETH1 = 4
• Mexican-American: RIDRETH1 = 1
• All Other Races/Ethnicities: RIDRETH1 = 2 or 5 or missing
The "All Other Races/Ethnicities" category includes multiracial persons and individuals whose
racial or ethnic identity is not White non-Hispanic, Black non-Hispanic, or Mexican-American.
Except for non-Mexican American Hispanics in 2007-2016 and Asian non-Hispanics in 2011-
2016, persons of "All Other Races/Ethnicities" are selected into the survey with a probability
that is very much lower than White non-Hispanic, Black non-Hispanic and Mexican American
individuals, and as a group they are not representative of all other race and ethnicities in the
United States.
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Biomonitoring: Phthalates
Calculation of Indicator
Indicator B9 is the median for urine phthalate metabolites in women of ages 16 to 49 years,
stratified by NHANES survey cycle. The median for women ages 16 to 49 is the estimated
concentration such that 50% of all non-institutionalized civilian women ages 16 to 49 years have
urine phthalate metabolites concentrations below this level. To adjust the NHANES data to
represent prenatal exposures, the data for each woman surveyed was multiplied by the estimated
number of births per woman of the given age and race/ethnicity. Indicator BIO is the median for
urine phthalate metabolites in children of ages 6 to 17 years, stratified by NHANES survey
cycle. The birth rate adjustment was not applied to children ages 6 to 17. Table B9a presents the
95th percentile for urine phthalate metabolites in women of ages 16 to 49 years, stratified by
NHANES survey cycle. The 95th percentile for women ages 16 to 49 is the estimated
concentration such that 95% of all non-institutionalized civilian women ages 16 to 49 years have
urine phthalate metabolites concentrations below this level. Table B9b presents the median for
urine phthalate metabolites in women of ages 16 to 49 years in 2013-2016, stratified by
race/ethnicity and family income. Table BlOa presents the 95th percentile for urine phthalate
metabolites in children of ages 6 to 17, stratified by NHANES survey cycle. Table B 10b presents
the median for urine phthalate metabolites in children of ages 6 to 17 years in 2013-2016,
stratified by race/ethnicity and family income. Table BlOc presents the median concentration of
phthalate metabolites for children ages 6 to 17 in 2013-2016, stratified by age group.
To simply demonstrate the calculations, we will use the NHANES 2007-2008 urine sum of MBP
and MIB (DBP = DBP metabolites) values for women ages 16 to 49 years of all race/ethnicities
and all incomes as an example. We have rounded all the numbers to make the calculations easier:
We begin with all the non-missing NHANES 2007-2008 urine DBP values for women ages 16 to
49 years. Assume for the sake of simplicity that valid DBP data were available for every sampled
woman. Each sampled woman has an associated annual survey weight that estimates the annual
number of U.S. women represented by that sampled woman. For 2007-2008, the associated
annual survey weight for each woman is defined as WTSB2YR. Each sampled woman also has
an associated birth rate giving the numbers of annual births per woman of the given age, race,
and ethnicity. The product of the annual survey weight and the birth rate estimates the annual
number of U.S. births represented by that sampled woman, which we will refer to as the adjusted
survey weight. For example, the lowest urine DBP measurement for a woman between 16 and 49
years of age is 0.6 |ig/L with an annual survey weight of 350,000, a birth rate of 0.0013, and thus
an adjusted survey weight of 450, and so represents 450 births. The total of the adjusted survey
weights for the sampled women equals 4 million, the total number of annual U.S. births to
women ages 16 to 49 years. The second lowest measurement is also 0.6 |ig/L with an adjusted
survey weight of 12,000, and so represents another 12,000 U.S. births. The highest measurement
is 788.9 |ig/L with an adjusted survey weight of 1,200, and so represents another 1,200 U.S.
births.
To calculate the median, we can use the adjusted survey weights to expand the data to the entire
U.S. population of births to women ages 16 to 49. We have 450 values of 0.6 |ig/L from the
lowest measurement, 12,000 values of 0.6 |ig/L from the second lowest measurement, and so on,
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up to 1,200 values of 788.9 |ig/L from the highest measurement. Arranging these 4 million
values in increasing order, the 2 millionth value is 36.3 |ig/L. Since half of the values are below
36.3 and half of the values are above 36.3, the median equals 36.3 |ig/L. To calculate the 95th
percentile, note that 95% of 4 million equals 3.8 million. The 3.8 millionth value is 160.2 |ig/L.
Since 95% of the values are below 160.2, the 95th percentile equals 160.2|ig/L.
In reality, the calculations need to take into account that urine DBP measurements were not
available for every respondent, and to use exact rather than rounded numbers. There were urine
DBP measurements for only 571 of the 589 sampled women ages 16 to 49 years. The adjusted
survey weights for all 589 sampled women add up to 4.2 million, the U.S. population of births to
women ages 16 to 49. The adjusted survey weights for the 571 sampled women with urine DBP
data add up to 4.1 million. Thus the available data represent 4.1 million values and so represent
only 98% of the U.S. population of births. The median and 95th percentiles are given by the 2.05
millionth (50% of 4.1 million) and 3.90 millionth (95% of 4.1 million) U.S. birth's value. These
calculations assume that the sampled women with valid urine DBP data are representative of
women giving birth without valid urine DBP data. The calculations also assume that the sampled
women are representative of women that actually gave birth in 2007-2008, since NHANES
information on pregnancy and births was not incorporated into the analysis.
Equations
These percentile calculations can also be given as the following mathematical equations, which
are based on the default percentile calculation formulas from Statistical Analysis System®
(SAS®) software. Exclude all missing urine DBP values. Suppose there are n women of ages 16
to 49 years with valid urine DBP values. Arrange the urine DBP concentrations in increasing
order (including tied values) so that the lowest concentration is x(l) with an adjusted survey
weight of w(l), the second lowest concentration is x(2) with an adjusted survey weight of w(2),
..., and the highest concentration is x(n) with an adjusted survey weight of w(n).
1. Sum all the adjusted survey weights to get the total weight W:
W = E[1 < i < n] w(i)
2. Find the largest number i so that the total of the weights for the i lowest values is less than or
equal to W/2.
E[j < i] w(j) < W/2 < E[j < i + 1] w(j)
3. Calculate the median using the results of the second step. We either have
E[j < i] w(j) = W/2 < E[j < i + 1] w(j)
or
E[j < i] w(j) < W/2 < E[j < i + 1] w(j)
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In the first case we define the median as the average of the i'th and i + l'th values:
Median = [x(i) + x(i + l)]/2 if S[j < i] w(j) = W/2
In the second case we define the median as the i + l'th value:
Median = x(i + 1) if E[j < i] w(j) < W/2
(The estimated median does not depend upon how the tied values of x(j) are ordered).
A similar calculation applies to the 95th percentile. The first step to calculate the sum of the
weights, W, is the same. In the second step, find the largest number i so that the total of the
weights for the i lowest values is less than or equal to 0.95W.
E[j < i] w(j) < 0.95W < E[j < i + 1] w(j)
In the third step we calculate the 95th percentile using the results of the second step. We either
have
E[j < i] w(j) = 0.95W < E[j < i + 1] w(j)
or
E[j < i] w(j) < 0.95W < E[j < i + 1] w(j)
In the first case we define the 95th percentile as the average of the i'th and i + l'th values:
95th Percentile = [x(i) + x(i + l)]/2 if S[j < i] w(j) = 0.95W
In the second case we define the 95th percentile as the i + l'th value:
95th Percentile = x(i + 1) if S[j < i] w(j) < 0.95W
Relative Standard Error
The uncertainties of the median and 95th percentile values were calculated using a revised
version of the CDC method given in CDC 2005,1V Appendix C, and the SAS® program provided
by CDC. The method uses the Clopper-Pearson binomial confidence intervals adapted for
complex surveys by Korn and Graubard (see Korn and Graubard, 1999,v p. 65). The following
text is a revised version of the Appendix C. For the birth rate adjusted calculations for women
ages 16 to 49, the sample weight is adjusted by multiplying by the age-specific birth rate.
1V CDC Third National Report on Human Exposure to Environmental Chemicals. 2005
v Korn E. L.. Graubard B. I. 1999. Analysis of Health Surveys. Wiley.
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Step 1: Use SAS® Proc Univariate to obtain a point estimate PSas of the percentile value. Use the Weight
option to assign the exact correct sample weight for each chemical result.
Step 2: Use SUDAAN® Proc Descript with Taylor Linearization DESIGN = WR (i.e.,
sampling with replacement) and the proper sampling weight to estimate the proportion (p) of subjects with
results less than and not equal to the percentile estimate Psas obtained in Step 1 and to obtain the standard
error (sep) associated with this proportion estimate. Compute the degrees-of-freedom adjusted effective
sample size
n,;lf = ( tnum/ tdenom )2 p (1 - p) / (sep 2)
where tri,m, and tdenom are 0.975 critical values of the Student's t distribution with degrees of freedom
equal to the sample size minus 1 and the number of primary sampling units (PSUs) minus the number of
strata, respectively. Note: the degrees of freedom for tdenom can vary with the demographic sub-group of
interest.
Step 3: After obtaining an estimate of p (i.e., the proportion obtained in Step 2), compute the Clopper-
Pearson 95% confidence interval (PL(x,ndf), Pu(x.ndf)) as follows:
PL(x,ndf) = ViFvi,v2 (0.025)/(v2 + ViFvi,v2(0.025))
Pu(x,ndf) = v3FV3,v4 (0.975)/(v4 + v3FV3,v4(0.975))
where x is equal to p times ndf, vi = 2x, v2 = 2(ndf - x + 1), v3 = 2(x + 1), v4 = 2(ndf - x), and Fn.,i:(P) is
the (3 quantile of an F distribution with dl and d2 degrees of freedom. (Note: If ndf is greater than the
actual sample size or if p is equal to zero, then the actual sample size should be used.) This step will
produce a lower and an upper limit for the estimated proportion obtained in Step 2.
Step 4: Use SAS® Proc Univariate (again using the Weight option to assign weights) to determine the
chemical percentile values Pcdc, LCdc and Ucdc that correspond to the proportion p obtained in Step 2 and
its lower and upper limits obtained in Step 3. Do not round the values of p and the lower and upper limits.
For example, if p = 0.4832, then Pcdc is the 48.32'th percentile value of the chemical. The alternative
percentile estimates Pcdc and Psas are not necessarily equal.
Step 5: Use the confidence interval from Step 4 to estimate the standard error of the estimated percentile
Pcdc:
Standard Error (Pcdc) = (Ucdc - LCdc) / (2tdenom)
Step 6: Use the estimated percentile Pcdc and the standard error from Step 4 to estimate the relative
standard error of the estimated percentile Pcdc:
Relative Standard Error (%) = [Standard Error (Pcdc) / Pcdc] x 100%
The tabulated estimated percentile is the value of Psas given in Step 1. The relative standard error is given
in Step 6, using Pcdc and its standard error.
The relative standard error depends upon the survey design. For this purpose, the public release
version of NHANES includes the variables SDMVSTRA and SDMVPSU, which are the Masked
Variance Unit pseudo-stratum and pseudo-primary sampling unit (pseudo-PSU). For
approximate variance estimation, the survey design can be approximated as being a stratified
random sample with replacement of the pseudo-PSUs from each pseudo-stratum; the true stratum
and PSU variables are not provided in the public release version to protect confidentiality. If the
relative standard error is too high, then the estimated percentile will not be accurately estimated.
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Furthermore, if the degrees of freedom (from Step 2) is too low, then the relative standard error
will be less accurately estimated and thus may be underestimated. For these reasons, percentiles
with high relative standard errors or with low degrees of freedom are unstable or unreliable.
Percentiles with a relative standard error less than 30% and with 12 or more degrees of freedom
were treated as being reliable and were tabulated. Percentiles with a relative standard error that is
30% or greater but less than 40% and with 12 or more degrees of freedom were treated as being
unstable; these values were tabulated but were flagged to be interpreted with caution. Percentiles
with a relative standard error less than 40% and with between 7 and 11 degrees of freedom were
also treated as being unstable; these values were tabulated but were flagged to be interpreted
with caution. Percentiles with a relative standard error that is 40% or greater, or without an
estimated relative standard error, or with 6 or less degrees of freedom, were treated as being
unreliable; these values were not tabulated and were flagged as having a large uncertainty.
Questions and Comments
Questions regarding these methods, and suggestions to improve the description of the methods,
are welcome. Please use the "Contact Us" link at the bottom of any page in the America's
Children and the Environment website.
Statistical Comparisons
Statistical analyses of the percentiles were used to determine whether the differences between
percentiles for different demographic groups were statistically significant. For these analyses, the
percentiles and their standard errors were calculated for each combination of age group, sex,
income group (below poverty, at or above poverty, unknown income), and race/ethnicity group
using the method described in the "Relative Standard Error" section. In the notation of that
section, the percentile and standard error are the values of Pcdc and Standard Error (Pcdc),
respectively. These calculated standard errors account for the survey weighting and design and,
for women, for the age-specific birth rate.
Using a weighted linear regression model, the percentile was assumed to be the sum of
explanatory terms for age, sex, income and/or race/ethnicity and a random error term; the error
terms were assumed to be approximately independent and normally distributed with a mean of
zero and a variance equal to the square of the standard error. In this model, the weight is the
inverse of the variance, so that percentiles with larger standard errors are given less of a
statistical weight in the fitted regression model. Using this model, the difference in the value of a
percentile between different demographic groups is statistically significant if the difference
between the corresponding sums of explanatory terms is statistically significantly different from
zero. A p-value at or below 0.05 implies that the difference is statistically significant at the 5%
significance level. No adjustment is made for multiple comparisons.
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For each type of comparison, we present unadjusted and adjusted analyses. The unadjusted
analyses directly compare a percentile between different demographic groups. The adjusted
analyses add other demographic explanatory variables to the statistical model and use the
statistical model to account for the possible confounding effects of these other demographic
variables. For example, the unadjusted race/ethnicity comparisons use and compare the
percentiles between different race/ethnicity pairs. The adjusted race/ethnicity comparisons use
the percentiles for each age/sex/income/race/ethnicity combination. The adjusted analyses add
age, sex, and income terms to the statistical model and compare the percentiles between different
race/ethnicity pairs after accounting for the effects of the other demographic variables. For
example, if White non-Hispanics tend to have higher family incomes than Black non-Hispanics,
and if the urine phthalate level strongly depends on family income only, then the unadjusted
differences between these two race/ethnicity groups would be significant but the adjusted
difference (taking into account income) would not be significant.
Comparisons between pairs of race/ethnicity groups are shown in Table 1 for women ages 16 to
49 years and in Table 4 for children ages 6 to 17 years. Comparisons between income groups are
shown in Table 2 for women ages 16 to 49 years and in Table 5 for children ages 6 to 17 years.
In Tables 1 and 4, for the unadjusted "All incomes" comparisons, the only explanatory variables
are terms for each race/ethnicity group. For these unadjusted comparisons, the statistical tests
compare the percentiles for each pair of race/ethnicity groups. For the adjusted "All incomes
(adjusted for age, sex, income)" comparisons, the explanatory variables are terms for each
race/ethnicity group together with terms for each age, sex (for children), and income group. For
these adjusted comparisons, the statistical test compares the pair of race/ethnicity groups after
accounting for any differences in the age, sex (for children) and income distributions between the
race/ethnicity groups. The adjustment for sex is applicable only to the analyses for children, and
thus appears only in Tables 4, 5, and 6.
In Tables 1 and 4, for the unadjusted "Below Poverty Level" and "At or Above Poverty Level"
comparisons, the only explanatory variables are terms for each of the twelve
race/ethnicity/income combinations (combinations of four race/ethnicity groups and three
income groups). For example, in row 1, the p-value for "Below Poverty Level" compares White
non-Hispanics below the poverty level with Black non-Hispanics below the poverty level. The
same set of explanatory variables are used in Tables 2 and 5 for the unadjusted comparisons
between one race/ethnicity group below the poverty level and the same race/ethnicity group at or
above the poverty level. The corresponding adjusted analyses include extra explanatory variables
for age and sex (for children), so that race/ethnicity/income groups are compared after
accounting for any differences due to age or sex. Although these comparisons only involve the
two income groups with known incomes, these statistical models were fitted to all three income
groups (including those with unknown income) to make a more general, better fitting model; this
approach has no impact on the unadjusted p-values but has a small impact on the adjusted p-
values. Also in Tables 2 and 5, the unadjusted p-value for the population "All" compares the
percentiles for women ages 16 to 49 years or children ages 6 to 17 years below poverty level
with those at or above poverty level, using the explanatory variables for the two income groups
(below poverty, at or above poverty), excluding those with unknown income. The adjusted p-
value includes adjustment terms for age, sex (for children), and race/ethnicity in the model.
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Additional comparisons are shown in Table 3 for women ages 16 to 49 years and in Table 6 for
children ages 6 to 17 years. Comparisons are shown for differences between children's age
groups, between those below poverty and those at or above poverty, and for changes over time
(trends). The Against = "age" unadjusted p-value compares the percentiles between children in
different age groups, using the explanatory variables for the age groups. The adjusted p-value
includes adjustment terms for sex (for children), race/ethnicity, and income in the model. The
Against = "income" unadjusted p-value compares the percentiles for those below poverty level
with those at or above poverty level, using the explanatory variables for the two income groups
(below poverty, at or above poverty). The adjusted p-value includes adjustment terms for age,
sex (for children), and race/ethnicity in the model. The Against = "year" p-value examines
whether the linear trend in the percentiles is statistically significant (using the percentiles for
each NHANES period regressed against the midpoint of that period); the adjusted model for
trend adjusts for demographic changes in the populations from year to year by including terms
for age, sex (for children), income, and race/ethnicity. The adjustment for sex is applicable only
for children, and thus appears only in Table 6.
For women, the age groups used were 16-19, 20-24, 25-29, 30-39, and 40-49. For children, the
age groups used were 6-10, 11-15, and 16-17.
For more details on these statistical analyses, see the memorandum by Cohen (2010).V1
Table 1. Statistical significance tests comparing the percentiles of phthalate metabolites in
women ages 16 to 49 years, between pairs of race/ethnicity groups, for 2013-2016.
P-VALUES
Variable
Percentile
First
race/ethnicity
group
Second
race/ethnicity
group*
All
incomes
All
incomes
(adjusted
for age,
income)
Below
Poverty
Level
Below
Poverty
Level
(adjusted
for age)
At or
Above
Poverty
Level
At or
Above
Povertj
Level
(adjuste
for age
DEHP
metabolites
50
White non-
Hispanic
Black non-
Hispanic
0.013
<0.001
0.059
0.008
0.070
0.00
DEHP
metabolites
50
White non-
Hispanic
Mexican
American
0.794
0.659
0.617
0.806
0.185
0.64
DEHP
metabolites
50
White non-
Hispanic
Other
0.057
0.531
0.257
0.067
0.342
0.15
DEHP
metabolites
50
Black non-
Hispanic
Mexican
American
0.026
0.003
0.251
0.009
0.008
0.08
DEHP
metabolites
50
Black non-
Hispanic
Other
<0.001
<0.001
0.005
0.182
0.010
<0.00
DEHP
metabolites
50
Mexican
American
Other
0.240
0.984
0.137
0.077
0.551
0.94
DBP
metabolites
50
White non-
Hispanic
Black non-
Hispanic
<0.001
0.001
0.013
0.207
0.080
0.02
DBP
metabolites
50
White non-
Hispanic
Mexican
American
0.971
0.659
0.475
0.753
0.299
0.50
V1 Cohen, J. 2010. Selected statistical methods for testing for trends and comparing years or demographic groups in
ACE NHIS and NHANES indicators. Memorandum submitted to Dan Axelrad, EPA, 21 March, 2010.
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P-VALUES
At or
All
Below
Above
First
Second
incomes
(adjusted
Below
Poverty
Level
At or
Above
Povertj
Level
Variable
Percentile
race/ethnicity
group
race/ethnicity
group*
All
incomes
for age,
income)
Poverty
Level
(adjusted
for age)
Poverty
Level
(adjuste
for age
DBP
metabolites
50
White non-
Hispanic
Other
0.767
0.258
0.905
0.139
0.573
0.71
DBP
metabolites
50
Black non-
Hispanic
Mexican
American
<0.001
<0.001
0.066
0.127
0.018
0.00
DBP
metabolites
50
Black non-
Hispanic
Other
0.004
<0.001
0.054
0.034
0.268
0.01
DBP
metabolites
50
Mexican
American
Other
0.749
0.481
0.668
0.198
0.182
0.68
BBzP
metabolite
50
White non-
Hispanic
Black non-
Hispanic
0.007
<0.001
0.150
0.002
0.284
0.75
BBzP
metabolite
50
White non-
Hispanic
Mexican
American
0.083
0.016
0.759
0.904
0.056
0.01
BBzP
metabolite
50
White non-
Hispanic
Other
0.091
<0.001
0.841
0.699
0.115
0.03
BBzP
metabolite
50
Black non-
Hispanic
Mexican
American
<0.001
<0.001
0.038
0.002
0.014
0.03
BBzP
metabolite
50
Black non-
Hispanic
Other
<0.001
<0.001
0.039
0.005
0.028
0.16
BBzP
metabolite
50
Mexican
American
Other
1.000
0.477
0.814
0.762
0.564
0.24
* "Other" represents the "All Other Races/Ethnicities" category, which includes all other races and ethnicities not specified, together with those
individuals who report more than one race.
Table 2. Statistical significance tests comparing the percentiles of phthalate metabolites in
women ages 16 to 49 years, between those below poverty level and those at or above poverty
level, for 2013-2016.
P-Values for difference
between income levels
Variable
Percentile
Population*
Unadjusted
Adjusted
(forage)**
DEHP
metabolites
50
All
0.056
<0.001
DEHP
metabolites
50
White non-Hispanic
0.321
0.390
DEHP
metabolites
50
Black non-Hispanic
0.064
0.085
DEHP
metabolites
50
Mexican American
0.032
0.525
DEHP
metabolites
50
Other
0.977
<0.001
DBP metabolites
50
All
0.071
0.003
DBP metabolites
50
White non-Hispanic
0.405
0.012
DBP metabolites
50
Black non-Hispanic
0.054
0.403
DBP metabolites
50
Mexican American
0.024
0.048
DBP metabolites
50
Other
0.726
0.658
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P-Values for difference
between income levels
Variable
Percentile
Population*
Unadjusted
Adjusted
(forage)**
BBzP metabolite
50
All
0.035
<0.001
BBzP metabolite
50
White non-Hispanic
0.572
0.878
BBzP metabolite
50
Black non-Hispanic
0.042
<0.001
BBzP metabolite
50
Mexican American
0.120
0.026
BBzP metabolite
50
Other
0.023
0.070
* "Other" represents the "All Other Races/Ethnicities" category, which includes all other races and ethnicities not specified, together with those
individuals who report more than one race.
** Comparison for "All" is adjusted for age and race/ethnicity; comparisons for race/ethnicity categories are adjusted for age.
Table 3. Other statistical significance tests comparing the percentiles of phthalate metabolites in
women ages 16 to 49 years, for 2013-2016 (trends for 1999-2016, 2007-2016, and 1999-2008).
P-VALUES
Variable
Percentile
From
To
Against
Unadjusted
Adjusted*
DEHP metabolites
50
2013
2016
income
0.056
<0.001
DEHP metabolites
50
2001
2016
year
<0.001
0.277
DEHP metabolites
50
2007
2016
year
<0.001
0.007
DEHP metabolites
50
2001
2008
year
0.758
0.134
DBP metabolites
50
2013
2016
income
0.071
0.003
DBP metabolites
50
1999
2016
year
<0.001
<0.001
DBP metabolites
50
2007
2016
year
0.020
NA**
DBP metabolites
50
1999
2008
year
0.168
<0.001
BBzP metabolite
50
2013
2016
income
0.035
<0.001
BBzP metabolite
50
1999
2016
year
<0.001
<0.001
BBzP metabolite
50
2007
2016
year
<0.001
<0.001
BBzP metabolite
50
1999
2008
year
0.112
<0.001
DEHP metabolites
95
2013
2016
income
0.107
<0.001
DEHP metabolites
95
2001
2016
year
<0.001
<0.001
DEHP metabolites
95
2007
2016
year
<0.001
<0.001
DEHP metabolites
95
2001
2008
year
0.693
0.066
DBP metabolites
95
2013
2016
income
0.929
0.057
DBP metabolites
95
1999
2016
year
<0.001
<0.001
DBP metabolites
95
1999
2008
year
0.092
<0.001
DBP metabolites
95
2007
2016
year
<0.001
<0.001
DBP metabolites
95
1999
2008
year
0.092
<0.001
BBzP metabolite
95
2013
2016
income
0.430
<0.001
BBzP metabolite
95
1999
2016
year
<0.001
<0.001
BBzP metabolite
95
2007
2016
year
0.968
<0.001
BBzP metabolite
95
1999
2008
year
0.089
<0.001
*For Against = "income," the comparison is between those below the poverty level and those at or above the poverty level, and the p-values are
adjusted for age and race/ethnicity.
For Against = "year" the comparison is the trend over different years, and the p-values are adjusted for age, race/ethnicity, and income.
**P-value is not available. Model convergence is questionable.
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Biomonitoring: Phthalates
Table 4. Statistical significance tests comparing the percentiles of phthalate metabolites in
children ages 6 to 17 years, between pairs of race/ethnicity groups, for 2013-2016.
P-VALUES
Variable
Percentile
First
race/ethnicity
group
Second
race/ethnicity
group*
All
incomes
All
incomes
(adjusted
for age,
income)
Below
Poverty
Level
Below
Poverty
Level
(adjusted
for age)
At or
Above
Poverty
Level
At or
Above
Poverty
Level
(adjusted
for age)
DEHP
metabolites
50
White non-
Hispanic
Black non-
Hispanic
<0.001
<0.001
0.031
<0.001
0.026
0.004
DEHP
metabolites
50
White non-
Hispanic
Mexican
American
0.012
<0.001
0.345
0.011
0.010
0.062
DEHP
metabolites
50
White non-
Hispanic
Other
0.246
0.305
0.559
0.893
0.615
0.968
DEHP
metabolites
50
Black non-
Hispanic
Mexican
American
0.262
<0.001
0.142
0.005
0.835
0.534
DEHP
metabolites
50
Black non-
Hispanic
Other
0.015
<0.001
0.217
<0.001
0.089
0.007
DEHP
metabolites
50
Mexican
American
Other
0.199
0.005
0.856
0.020
0.047
0.081
DBP
metabolites
50
White non-
Hispanic
Black non-
Hispanic
0.486
<0.001
0.678
<0.001
0.633
0.733
DBP
metabolites
50
White non-
Hispanic
Mexican
American
0.247
0.036
0.076
0.023
0.531
0.001
DBP
metabolites
50
White non-
Hispanic
Other
0.248
<0.001
0.232
0.622
0.200
0.069
DBP
metabolites
50
Black non-
Hispanic
Mexican
American
0.081
<0.001
0.046
<0.001
0.751
<0.001
DBP
metabolites
50
Black non-
Hispanic
Other
0.089
<0.001
0.138
<0.001
0.313
0.022
DBP
metabolites
50
Mexican
American
Other
0.913
0.072
0.800
0.013
0.603
0.134
BBzP
metabolite
50
White non-
Hispanic
Black non-
Hispanic
0.207
<0.001
0.431
<0.001
0.452
0.611
BBzP
metabolite
50
White non-
Hispanic
Mexican
American
0.356
0.316
0.368
0.123
0.612
0.288
BBzP
metabolite
50
White non-
Hispanic
Other
0.049
0.108
0.377
0.696
0.003
0.002
BBzP
metabolite
50
Black non-
Hispanic
Mexican
American
0.023
<0.001
0.010
<0.001
0.159
0.045
BBzP
metabolite
50
Black non-
Hispanic
Other
0.001
<0.001
0.013
<0.001
<0.001
<0.001
BBzP
metabolite
50
Mexican
American
Other
0.162
0.005
1.000
0.209
0.014
0.029
* "Other" represents the "All Other Races/Ethnicities" category, which includes all other races and ethnicities not specified, together with those
individuals who report more than one race.
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Biomonitoring: Phthalates
Table 5. Statistical significance tests comparing the percentiles of phthalate metabolites in
children ages 6 to 17 years, between those below poverty level and those at or above poverty
level, for 2013-2016.
P-Values for difference between income levels
Variable
Percentile
Population*
Unadjusted
Adjusted (for age,
sex)**
DEHP
metabolites
50
All
0.201
0.400
DEHP
metabolites
50
White non-Hispanic
0.858
0.048
DEHP
metabolites
50
Black non-Hispanic
0.280
0.031
DEHP
metabolites
50
Mexican American
0.455
0.683
DEHP
metabolites
50
Other
0.734
0.112
DBP metabolites
50
All
0.483
0.001
DBP metabolites
50
White non-Hispanic
0.233
<0.001
DBP metabolites
50
Black non-Hispanic
0.087
<0.001
DBP metabolites
50
Mexican American
0.709
0.042
DBP metabolites
50
Other
0.721
0.039
BBzP metabolite
50
All
0.061
0.003
BBzP metabolite
50
White non-Hispanic
0.358
0.253
BBzP metabolite
50
Black non-Hispanic
0.020
<0.001
BBzP metabolite
50
Mexican American
0.532
0.157
BBzP metabolite
50
Other
0.006
0.047
* "Other" represents the "All Other Races/Ethnicities" category, which includes all other races and ethnicities not specified, together with those
individuals who report more than one race.
* * Comparison for "All" is adjusted for age, sex, and race/ethnicity; comparisons for race/ethnicity categories are adjusted for age and sex.
Table 6. Other statistical significance tests comparing the percentiles of phthalate metabolites in
children ages 6 to 17 years, for 2013-2016 (trends for 1999-2016, 2007-2016, and 2001-2008).
P-VALUES
Variable
Percentile
From
To
Against
Unadjusted
Adjusted*
DEHP metabolites
50
2013
2016
age
0.013
0.028
DEHP metabolites
50
2013
2016
income
0.201
0.400
DEHP metabolites
50
2001
2016
year
<0.001
<0.001
DEHP metabolites
50
2007
2016
year
<0.001
<0.001
DEHP metabolites
50
2001
2008
year
0.382
<0.001
DBP metabolites
50
2013
2016
age
0.230
<0.001
DBP metabolites
50
2013
2016
income
0.483
0.001
DBP metabolites
50
1999
2016
year
<0.001
<0.001
DBP metabolites
50
2007
2016
year
<0.001
<0.001
DBP metabolites
50
1999
2008
year
0.247
<0.001
BBzP metabolite
50
2013
2016
age
0.030
<0.001
BBzP metabolite
50
2013
2016
income
0.061
0.003
BBzP metabolite
50
1999
2016
year
<0.001
<0.001
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Biomonitoring: Phthalates
P-VALUES
Variable
Percentile
From
To
Against
Unadjusted
Adjusted*
BBzP metabolite
50
2007
2016
year
<0.001
<0.001
BBzP metabolite
50
1999
2008
year
<0.001
<0.001
DEHP metabolites
95
2013
2016
age
0.021
<0.001
DEHP metabolites
95
2013
2016
income
0.195
<0.001
DEHP metabolites
95
2001
2016
year
<0.001
<0.001
DEHP metabolites
95
2007
2016
year
<0.001
<0.001
DEHP metabolites
95
2001
2008
year
0.043
<0.001
DBP metabolites
95
2013
2016
age
0.832
<0.001
DBP metabolites
95
2013
2016
income
0.398
<0.001
DBP metabolites
95
1999
2016
year
<0.001
<0.001
DBP metabolites
95
2007
2016
year
<0.001
0.094
DBP metabolites
95
1999
2008
year
<0.001
<0.001
BBzP metabolite
95
2013
2016
age
0.193
<0.001
BBzP metabolite
95
2013
2016
income
0.017
<0.001
BBzP metabolite
95
1999
2016
year
<0.001
<0.001
BBzP metabolite
95
2007
2016
year
0.019
<0.001
BBzP metabolite
95
1999
2008
year
<0.001
<0.001
*For Against = "age," the comparison is between the age groups 6-10, 11-15, and 16-17 years, and the p-values are adjusted for sex,
race/ethnicity, and income.
For Against = "income," the comparison is between those below the poverty level and those at or above the poverty level, and the p-values are
adjusted for age, sex, and race/ethnicity.
For Against = "year" the comparison is the trend over different years, and the p-values are adjusted for age, sex, race/ethnicity, and income.
Data Files
The following files are needed to calculate this indicator."1 The files together with the survey
documentation and SAS® programs for reading in the data are available at the NHANES
website: http://www.cdc.gov/nchs/nhanes.htm.
• NHANES 1999-2000: Demographic file demo.xpt. Urinary Phthalates, Urinary PAHs,
and Urinary Phytoestrogens Laboratory file phpypa.xpt. The demographic file demo.xpt
is a SAS® transport file that contains the subject identifier (SEQN), age (RIDAGEYR),
sex (RIAGENDR), race/ethnicity (RIDRETH1), poverty income ratio (INDFMPIR),
pseudo-stratum (SDMVSTRA) and the pseudo-PSU (SDMVPSU). The Urinary
Phthalates, Urinary PAHs, and Urinary Phytoestrogens laboratory file phpypa.xpt
contains SEQN, the three phthalate metabolite concentrations (URXMBP, URXMZP,
URXMHP), and the two-year Mobile Examination Center (MEC) sub-sample weight
(WTSPH2YR). The two files are merged using the common variable SEQN.
• NHANES 2001-2002: Demographic file demo_b.xpt. Urinary Phthalates, Urinary PAHs,
and Urinary Phytoestrogens Laboratory file phpypa b.xpt. The demographic file
demo b.xpt is a SAS® transport file that contains the subject identifier (SEQN), age
vu On February 1, 2012, CDC announced that a correction factor needed to be applied to each value for certain
phthalate metabolites, including mono-benzyl phthalate (MBzP). The correction factor for MBzP is 0.72, and is
applicable to each MBzP measurement for NHANES survey periods 1999-2000, 2001-2002, 2003-2004, 2005-2006,
and 2007-2008. This correction was applied to the MBzP values presented in ACE3.
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(RIDAGEYR), sex (RIAGENDR), race/ethnicity (RIDRETH1), poverty income ratio
(INDFMPIR), pseudo-stratum (SDMVSTRA) and the pseudo-PSU (SDMVPSU). The
Urinary Phthalates, Urinary PAHs, and Urinary Phytoestrogens laboratory file
phpypa b.xpt contains SEQN, the six phthalate metabolite concentrations (URXMBP,
URXMIB, URXMZP, URXMHP, URXMOH, URXMHH), and the two-year MEC sub-
sample weight (WTSPH2YR). The two files are merged using the common variable
SEQN.
• NHANES 2003-2004: Demographic file demo_c.xpt. Urinary Phthalates Laboratory file
124ph_c.xpt. The demographic file demo c.xpt is a SAS® transport file that contains the
subject identifier (SEQN), age (RIDAGEYR), sex (RIAGENDR), race/ethnicity
(RIDRETH1), poverty income ratio (INDFMPIR), pseudo-stratum (SDMVSTRA) and
the pseudo-PSU (SDMVPSU). The Urinary Phthalates laboratory file 124ph_c.xpt
contains SEQN, the six phthalate metabolite concentrations (URXMBP, URXMIB,
URXMZP, URXMHP, URXMOH, URXMHH), the six phthalate metabolite non-detect
comment codes (URDMBPLC, URDMIBLC, URDMZPLC, URDMHPLC,
URDMOHLC, URDMHHLC), and the two-year MEC sub-sample B weight
(WTSB2YR). The two files are merged using the common variable SEQN.
• NHANES 2005-2006: Demographic file demod.xpt. Urinary Phthalates Laboratory file
phthted.xpt. The demographic file demo d.xpt is a SAS® transport file that contains the
subject identifier (SEQN), age (RIDAGEYR), sex (RIAGENDR), race/ethnicity
(RIDRETH1), poverty income ratio (INDFMPIR), pseudo-stratum (SDMVSTRA) and
the pseudo-PSU (SDMVPSU). The Urinary Phthalates laboratory file phthte d.xpt
contains SEQN, the six phthalate metabolite concentrations (URXMBP, URXMIB,
URXMZP, URXMHP, URXMOH, URXMHH), the six phthalate metabolite non-detect
comment codes (URDMBPLC, URDMIBLC, URDMZPLC, URDMHPLC,
URDMOHLC, URDMHHLC), and the two-year MEC sub-sample B weight
(WTSB2YR). The two files are merged using the common variable SEQN.
• NHANES 2007-2008: Demographic file demo_e.xpt. Urinary Phthalates Laboratory file
phthtee.xpt. The demographic file demo e.xpt is a SAS® transport file that contains the
subject identifier (SEQN), age (RIDAGEYR), sex (RIAGENDR), race/ethnicity
(RIDRETH1), poverty income ratio (INDFMPIR), pseudo-stratum (SDMVSTRA) and
the pseudo-PSU (SDMVPSU). The Urinary Phthalates laboratory file phthte e.xpt
contains SEQN, the six phthalate metabolite concentrations (URXMBP, URXMIB,
URXMZP, URXMHP, URXMOH, URXMHH), the six phthalate metabolite non-detect
comment codes (URDMBPLC, URDMIBLC, URDMZPLC, URDMHPLC,
URDMOHLC, URDMHHLC), and the two-year MEC sub-sample B weight
(WTSB2YR).
• NHANES 2009-2010: Demographic file demof. xpt. Phthalates - Urine Laboratory file
phthte f.xpt. The demographic file demo f.xpt is a SAS® transport file that contains the
subject identifier (SEQN), age (RIDAGEYR), sex (RIAGENDR), race/ethnicity
(RIDRETH1), poverty income ratio (INDFMPIR), pseudo-stratum (SDMVSTRA) and
the pseudo-PSU (SDMVPSU). The Phthalates - Urine laboratory file phthtef xpt
contains SEQN, the six phthalate metabolite concentrations (URXMBP, URXMIB,
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URXMZP, URXMHP, URXMOH, URXMHH), the six phthalate metabolite non-detect
comment codes (URDMBPLC, URDMIBLC, URDMZPLC, URDMHPLC,
URDMOHLC, URDMHHLC), and the two-year MEC sub-sample B weight
(WTSB2YR). The two files are merged using the common variable SEQN.
• NHANES 2011-2012: Demographic file demo_g.xpt. Phthalates & Plasticizers
Metabolites - Urine Laboratory file phthteg.xpt. The demographic file demo g.xpt is a
SAS® transport file that contains the subject identifier (SEQN), age (RIDAGEYR), sex
(RIAGENDR), race/ethnicity (RIDRETH1), poverty income ratio (INDFMPIR), pseudo-
stratum (SDMVSTRA) and the pseudo-PSU (SDMVPSU). The Phthalates & Plasticizers
Metabolites - Urine laboratory file phthte g.xpt contains SEQN, the six phthalate
metabolite concentrations (URXMBP, URXMIB, URXMZP, URXMHP, URXMOH,
URXMHH), the six phthalate metabolite non-detect comment codes (URDMBPLC,
URDMIBLC, URDMZPLC, URDMHPLC, URDMOHLC, URDMHHLC), and the two-
year MEC sub-sample A weight (WTSA2YR). The two files are merged using the
common variable SEQN.
• NHANES 2013-2014: Demographic file demoh.xpt. Phthalates & Plasticizers
Metabolites - Urine Laboratory file phthteh.xpt. The demographic file demo h.xpt is a
SAS® transport file that contains the subject identifier (SEQN), age (RIDAGEYR), sex
(RIAGENDR), race/ethnicity (RIDRETH1), poverty income ratio (INDFMPIR), pseudo-
stratum (SDMVSTRA) and the pseudo-PSU (SDMVPSU). The Phthalates & Plasticizers
Metabolites - Urine laboratory file phthte h.xpt contains SEQN, the six phthalate
metabolite concentrations (URXMBP, URXMIB, URXMZP, URXMHP, URXMOH,
URXMHH), the six phthalate metabolite non-detect comment codes (URDMBPLC,
URDMIBLC, URDMZPLC, URDMHPLC, URDMOHLC, URDMHHLC), and the two-
year MEC sub-sample B weight (WTSB2YR). The two files are merged using the
common variable SEQN.
• NHANES 2015-2016: Demographic file demoi.xpt. Phthalates & Plasticizers
Metabolites - Urine Laboratory file phthtei.xpt. The demographic file demo i.xpt is a
SAS® transport file that contains the subject identifier (SEQN), age (RIDAGEYR), sex
(RIAGENDR), race/ethnicity (RIDRETH1), poverty income ratio (INDFMPIR), pseudo-
stratum (SDMVSTRA) and the pseudo-PSU (SDMVPSU). The Phthalates & Plasticizers
Metabolites - Urine laboratory file phthte i.xpt contains SEQN, the six phthalate
metabolite concentrations (URXMBP, URXMIB, URXMZP, URXMHP, URXMOH,
URXMHH), the six phthalate metabolite non-detect comment codes (URDMBPLC,
URDMIBLC, URDMZPLC, URDMHPLC, URDMOHLC, URDMHHLC), and the two-
year MEC sub-sample B weight (WTSB2YR). The two files are merged using the
common variable SEQN.
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