Behavioral Ecology Vol. 14 No. 3: 446-447
© 2003 International Society for Behavioral Ecology
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Confidence intervals are a more useful complement to nonsignificant tests than are power calculations
a ICAPB, University of Edinburgh, Ashworth Laboratory, Kings Building, west Mains Road, Edinburgh, EH9 3JT, UK b Division of Environmental and Evolutionary Biology IBLS, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ, Glasgow, UK
Address correspondence to N. Colegrave. E-mail: n.colegrave@ed.ac.uk.
Received 21 June 2002; revised 29 September 2002; accepted 1 October 2002.
| The first 150 words of the full text of this article appear below. |
Many leading journals, including Behavioral Ecology, emphasize the importance of considering the power of statistical tests in the light of nonsignificant results. However, there is considerable scope for misinterpretation of what this advice actually implies. The common conception among biologists is that a nonsignificant result with low power is not to be relied on, but a nonsignificant result with high power is strong support for the null hypothesis. Here we will draw on a recent paper by Hoenig and Heisey (2001)
to explain why use of (post hoc) power analysis actually provides no more information than does the p value itself.
Imagine we are interested in knowing whether the type of bean on which a beetle larva develops affects the size of the beetle as an adult. We raise 10 beetle larvae on black-eyed beans and 10 on mung beans, and we measure their size as adults. The mean size
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