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Adequacy of sample size for estimating a value from field observational data.
Susan M Cormier1, Glenn W Suter1, Mark B Fernandez2
1Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH, 45268, USA.
Ecotoxicology and Environmental Safety
|August 11, 2020
Summary
This study re-evaluates aquatic life benchmarks for conductivity, confirming their validity against claims of small sample size bias. Evidence supports the benchmark
Area of Science:
- Environmental Science
- Ecotoxicology
- Water Quality Assessment
Background:
- A 2011 U.S. EPA method for aquatic life conductivity benchmarks has been widely supported.
- Recent challenges questioned the method's validity, citing small sample sizes.
Purpose of the Study:
- To address the hypothesis that the conductivity benchmark is a statistical artifact due to sample size.
- To supplement prior causal analyses with new evidence.
Main Methods:
- Permutation analyses to assess data set reliability for estimating genus extirpation.
- Analysis of genus occurrence sufficiency for extirpation estimation.
- Ecological explanations for observed community patterns.
- Review of independent studies supporting the benchmark.
Main Results:
- Data sets reliably estimate the extirpation of 5% of genera.
- 25 genus occurrences are sufficient for extirpation estimation.
- Community ecology, not sample size, explains benchmark influences.
- Independent studies corroborate the benchmark's validity.
Conclusions:
- The conductivity benchmark is not a statistical artifact of sample size.
- Permutation tests are valuable for assessing field data adequacy.
- This weight-of-evidence approach can model other field-based benchmarks.
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