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Optimum Sample Size to Detect Perturbation Effects: The Importance of Statistical Power Analysis – A Critique
Author(s) -
Ortiz Marco
Publication year - 2002
Publication title -
marine ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.668
H-Index - 58
eISSN - 1439-0485
pISSN - 0173-9565
DOI - 10.1046/j.1439-0485.2002.02735.x
Subject(s) - sample size determination , statistical power , statistics , power analysis , a priori and a posteriori , econometrics , statistical hypothesis testing , statistical analysis , marine ecosystem , sample (material) , mathematics , computer science , ecosystem , ecology , physics , algorithm , biology , cryptography , thermodynamics , philosophy , epistemology
. The current article describes statistical power analysis as an efficient strategy for the estimation of the optimum sample size. The principle aim is constructively to criticise and enrich the results presented by Mouillot et al. (1999), who estimate the optimum sample size for evaluating possible perturbations. The authors did not make any reference to statistical power analysis, even though their objective clearly went beyond a simple stock evaluation to assess management strategies in a particular marine ecosystem. Surprisingly, they proposed ( a priori ) an ANOVA design to test a hypothesis considering both space and temporal scales. However, the authors did not cover important topics related with power analysis and the precautionary principle, both used into environment impact assessment programmes for marine ecosystems. Based on their results and on statistical power analysis, it is demonstrated that the variability (dispersion statistics), a key factor they used to estimate the sample size, is less relevant than the magnitude of perturbation (effect size). Therefore, a greater effort must be devoted to estimate the effect size of a particular phenomenon rather than a desired variability.