ERRATA—Replaces page 100 of EPA/630/R-00/002
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components are present in equitoxic amounts. This assumption is also explicit in Finney's model
of a deviation from dose additivity (e.g., Finney, 1971, Equation 11.83, p. 262).

4.3.1.7. Example
       The properties of the interaction-based HI and some sample calculations are presented in
this section, using hypothetical chemicals so that certain points can be illustrated. Consider the
following scenarios where high-quality information is known on the binary interactions of the
mixture components. In all three cases, the weight-of-evidence categories would be I and thus
the WOE scores would be 1.0.
       Scenario 1         ;
       All binary combinations of three  chemicals are known to synergize each other by a factor
       of 5 for the route and duration of concern, with an interaction directly relevant to human
       health.
       Scenario 2
       All binary combinations of three  chemicals are known to be additive for the route and
       duration of concern, with an interaction directly relevant to human health.
       Scenario 3
       All binary combinations of three  chemicals are known to antagonize each other by a
       factor of 5 for the route and duration of concern, with an interaction directly relevant to
       human health.
       In scenario 2, each B^ is equal to  zero because the three chemicals are known to be
additive (category IV-C in Table 4-3). As a result, M is taken to the power of zero. Thus,
whatever default value is used for M, the value of M to the power of zero is unity.  Also, from
Equation 4-16 we see that regardless of the ratios of the components in the mixture, the sum of
the fyS will equal 1.

                                                -  HQ)
In other words, the HI will not change from one based on additivity.  The HI modified for
interactions for scenario 2 is then:
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