Abstract

Although generally misunderstood, the p value is the probability of the test results or more extreme results given H-0 is true: it is not the probability of H-0 being true given the results. To obtain directly useful insight about H-0, the positive predictive value (PPV) and the negative predictive value (NPV) may be useful extensions of null hypothesis significance testing (NHST). They provide information about the probability of statistically significant and non-significant test outcomes being true based on an a priori defined biologically meaningful effect size. The present study explores the utility of PPV and NPV in an ecotoxicological context by using the frequently applied Daphnia magna reproduction test (OECD guideline 211) and the chemical stressor lindane as a model system. The results indicate that especially the NPV deviates meaningfully between a test design strictly following the guideline and an experimental procedure controlling for alpha and beta at the level of 0.05. Consequently, PPV and NPV may be useful supplements to NHST that inform the researcher about the level of confidence warranted by both statistically significant and non-significant test results. This approach also reinforces the value of considering alpha, beta, and a biologically meaningful effect size a priori.

Keywords

Sample size; Bayesian; Power analysis; Effect size; Type I error rate; Type II error rate

Published in

Environmental Science and Pollution Research
2013, Volume: 20, number: 10, pages: 7341-7347
Publisher: SPRINGER HEIDELBERG

SLU Authors

• Bundschuh, Mirco

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    
  • University of Koblenz-Landau

Sustainable Development Goals

SDG3 Ensure healthy lives and promote well-being for all at all ages


UKÄ Subject classification

Other Biological Topics


Publication identifier

DOI: https://doi.org/10.1007/s11356-013-1749-z

Permanent link to this page (URI)

https://res.slu.se/id/publ/50482