Created 8/xx/2005 Created by Dan McKenzie Luckiamute Watershed Survey Design This document is presented as an example and recommended format for documenting a GRTS design. It is recommended that this example be followed, prior to initiating efforts to produce a design to meet a particular objective. Due to the randomization scheme within psurvey.design, each execution of the R code will produce a different set of sampling points and output files and will not exactly reproduce the example files. Materials needed for this example: R version 2.0 or later psurvey.design package R script or text file: luckiamutedesign.R Frame materials as ArcGis files: luck-ash.dbf luck-ash. prj luck-ash. sbn luck-ash. sbx luck-ash. shp luck-ash., shx Example includes: Designs files produced 1 Equal Sites - 50 sites, equal wts Equal Sites.dbf Equal Sites.pij Equal Sites.shp Equal Sites.shx 2 Stratified Sites - Perennial 50 sites, Oversample 50 sites, Intermittent 50 sites, Oversample 50 sites. Stratified Sites.dbf Stratified Sites.prj Stratified Sites.shp Stratified Sites.shx) 3 Unequal Sites - Perennial w/ 3 Strahler categories (25,25,25 sites) plus Oversample (36) - Intermittent w/ 3 Strahler categories (17,5,3 sites) Unequal Sites.dbf Unequal Sites.prj Unequal Sites.shp Unequal Sites.shx 4 Panel Over Time Sites - Perennial w/ 3 Strahler categories (17,17,16), Oversample (50) - Intermittent w/ 3 Strahler (17,5,3) Panel Sites.dbf Panel Sites.prj Panel Sites, shp Panel Sites, shx) An ArcGis map is included, Luckiamute Design, as a visual aid for the resulting designs for this example. Design File Documentation would routinely begin here: Page 1 of 7 ------- Created 8/xx/2005 Created by Dan McKenzie Contact: Name address of person requesting the design Voice: Fax: email: Description of Sample Design Survey Design: A Generalized Random Tessellation Stratified (GRTS) survey design for a linear stream resource is used for this example. The GRTS design includes reverse hierarchical ordering of the selected sites. Target population: All perennial and intermittent streams/rivers in the Luckiamute Watershed Council basin. Watershed boundaries defined by Luckiamute Watershed Council. Sample Frame: GIS stream network coverage from PNW portion of RF3. [Example files: luck-ash, including Luckmap (ArcGis map)] Sample Frame Summary The total stream length (km) is 822.4882 km (including intermittent). Lengt l (km) Strahler Order Perennial Intermittent 0 10.64198 10.825986 1 189.88902 294.699772 2 133.10086 20.512487 3 60.84859 3.027805 4 68.24550 0 5 30.69616 0 3+4+5 159.79025 3.027805 Multi-density categories: Strahler order categories: 1st, 2nd, and 3rd+. I. Equal Probability GRTS Survey Design Stratification: None Expected sample size: 50 sites Oversample: None Site Use: The base design has 50 sites. Sites are listed in SitelD order and must be used in that order. All sites that occur prior to the last site used must have been evaluated for use and then either sampled or reason documented why that site was not used. Page 2 of 7 ------- Created 8/xx/2005 Created by Dan McKenzie Site Selection Summary Equal Probability Strahler Order 1 Strahler Order 2 Strahler Order 3+ Perennial 11 7 14 Intermittent 16 2 0 Total 27 9 14 II. Stratified GRTS Survey Design with Over Sample Stratification: Stratify by Perennial and Intermittent streams. Expected sample size: 50 sites for Perennial stratum and 50 sites for Intermittent stratum, plus in each stratum, sites selected with equal probability within stratum. Oversample: 50 sites for Perennial stratum and 50 sites for Intermittent stratum. Site Use: The stratified design has 50 sites, plus an over sample of 50 sites, in each stratum. Sites are listed in SitelD order and must be used in that order. All sites that occur prior to the last site used must have been evaluated for use and then either sampled or reason documented why that site was not used. Site Selection Summary Stratified Strahler 0 Strahler 1 Strahler 2 Strahler 3+ Total Perennial 1 17 17 15 50 Intermittent 1 43 6 0 50 Over Sample Perennial 1 20 10 19 50 Intermittent 3 42 5 0 50 III. Unequal Probability GRTS Survey Design with Over Sample and Stratification Stratification: Stratify by Perennial and Intermittent streams. Expected sample size: 75 sites with approximately an equal number within each Strahler order category for Perennial stratum. For Intermittent stratum, 25 sites with an expected sample size of 17, 5, and 3 for Strahler order categories 1st, 2nd, and 3rd+, respectively. Oversample: 36 sites for Perennial stratum and none for Intermittent stratum. Site Use: The unequal probability design has 75 sites, plus an over sample of 36 sites, for the Perennial stratum and 25 sites for the Intermittent stratum. Sites are listed in Page 3 of 7 ------- Created 8/xx/2005 Created by Dan McKenzie SitelD order and must be used in that order. All sites that occur prior to the last site used must have been evaluated for use and then either sampled or reason documented why that site was not used. Site Selection Summary Unequal Strahler 0+1 Strahler 2 Strahler 3+ Total Perennial 18 32 25 75 Intermittent 16 5 4 25 Over Sample Perennial 12 11 13 36 IV. Panels for Surveys Over Time with Unequal Probability GRTS Design with Over Sample and Stratification. Stratification: Stratify by Perennial and Intermittent streams. Panels: For Perennial stratum, three panels. Yearl sites will be visited in year 1 and then year 3, year 5, etc. Year2 sites will be visited in year 2, year 4, year 6, etc. YearAll sites will be visited every year. Intermittent stratum has a single panel of sites that will be visited only once. Expected sample size: 50 sites with approximately an equal number within each Strahler order category for Perennial stratum. For Intermittent stratum, 25 sites with an expected sample size of 17, 5, and 3 for Strahler order categories 1st, 2nd, and 3rd+, respectively. Oversample: 50 sites for Perennial stratum and none for Intermittent stratum. Site Use: The base design has 50 sites in Perennial stratum. Sites are listed in SitelD order and must be used in that order. All sites that occur prior to the last site used must have been evaluated for use and then either sampled or reason documented why that site was not used. As an example, if 30 sites are to be sampled in the watershed, then the first 30 sites in SitelD order would be used. Site Selection Summary Perennial Sites Panel Strahler 0+1 Strahler 2 Strahler 3+ Total Yearl 7 4 6 17 Year2 7 4 6 17 YearAll 6 4 6 16 OverSamp 15 17 18 50 Sum 35 29 36 100 Page 4 of 7 ------- Created 8/xx/2005 Created by Dan McKenzie Intermittent Sites Panel Strahler 0+1 Strahler 2 Strahler 3+ Total YearOnce 17 5 3 25 Description of Sample Design Output: The sites are provided as a shapefile that can be read directly by ArcMap. The dbf file associated with the shapefile may be read by Excel. The dbf file has the following variable definitions: Variable Name Description SitelD Unique site identification (character) arcid Internal identification number X Albers x-coordinate y Albers y-coordinate mdcaty Multi-density categories used for unequal probability selection weight Weight (in meters), inverse of inclusion probability, to be used in statistical analyses stratum Strata used in the survey design panel Identifies base sample by panel name and Oversample by OverS amp auxiliary variables Remaining columns are from the sample frame provided Luckiamute Design is an ArcMap that displays the stream network and sampling sites for the 4 example designs. Projection Information PROJCS["Clarke_1866_Albers", GEOGCS["GCS_Clarke_1866", DATUM["D_Clarke_l 866", SPHEROID["Clarke_1866",6378206.4,294.9786982]], PRIMEM [" Green wi ch", 0.0 ], UNIT["Degree",0.0174532925199433]], PROJECTION["Albers"], PARAMETER["False_Easting",0.0], PARAMETER["False_Northing",0.0], PARAMETER["Central_Meridian",-96.0], PARAMETER[" StandardParallell ",29.5], PARAMETER[" Standard_Parallel_2",45.5], PARAMETER["Latitude_Of_Ori gin",23.0], UNIT["Meter", 1.0]] Page 5 of 7 ------- Created 8/xx/2005 Created by Dan McKenzie Evaluation Process The survey design weights that are given in the design file assume that the survey design is implemented as designed. That is, only the sites that are in the base sample (not in the over sample) are used, and all of the base sites are used. This may not occur due to (1) sites not being a member of the target population, (2) landowners deny access to a site, (3) a site is physically inaccessible (safety reasons), or (4) site not sampled for other reasons. Typically, users prefer to replace sites that can not be sampled with other sites to achieve the sample size planned. The site replacement process is described above. When sites are replaced, the survey design weights are no longer correct and must be adjusted. The weight adjustment requires knowing what happened to each site in the base design and the over sample sites. EvalStatus is initially set to "NotEval" to indicate that the site has yet to be evaluated for sampling. When a site is evaluated for sampling, then the EvalStatus for the site must be changed. Recommended codes are: EvalStatus Code Name Meaning TS Target Sampled site is a member of the target population and was sampled LD Landowner Denial landowner denied access to the site PB Physical Barrier physical barrier prevented access to the site NT Non-Target site is not a member of the target population NN Not Needed site is a member of the over sample and was not evaluated for sampling Other codes Many times useful to have other codes. For example, rather than use NT, may use specific codes indicating why the site was non-target. Statistical Analysis Any statistical analysis of data must incorporate information about the monitoring survey design. In particular, when estimates of characteristics for the entire target population are computed, the statistical analysis must account for any stratification or unequal probability selection in the design. Procedures for doing this are available from the Aquatic Resource Monitoring web page given in the bibliography. A statistical analysis library of functions is available from the Aquatic Resource Monitoring web page to do common population estimates in the statistical software environment R (psurvey.analysis) ARM Web Page: http://www.epa.gov/nheerl/arm For further information, contact Anthony (Tony) R. 01 sen USEPA NHEERL Western Ecology Division 200 S.W. 35th Street Corvallis, OR 97333 Voice: (541) 754-4790 Page 6 of 7 ------- Created 8/xx/2005 Created by Dan McKenzie Fax:(541) 754-4716 email: 01sen.Tony@epa.gov Bibliography: Diaz-Ramos, S., D. L. Stevens, Jr, and A. R. Olsen. 1996. EMAP Statistical Methods Manual. EPA/620/R-96/002, U.S. Environmental Protection Agency, Office of Research and Development, NHEERL-Western Ecology Division, Corvallis, Oregon. Stevens, D.L., Jr. 1997. Variable density grid-based sampling designs for continuous spatial populations. Environmetrics, 8:167-95. Stevens, D.L., Jr. and Olsen, A.R. 1999. Spatially restricted surveys overtime for aquatic resources. Journal of Agricultural, Biological, and Environmental Statistics, 4:415-428 Stevens, D. L., Jr., and A. R. Olsen. 2003. Variance estimation for spatially balanced samples of environmental resources. Environmetrics 14:593-610. Stevens, D. L., Jr., and A. R. Olsen. 2004. Spatially-balanced sampling of natural resources in the presence of frame imperfections. Journal of American Statistical Association:99:262-278. Page 7 of 7 ------- |