The power of analysis: statistical perspectives. Part 1.
Failure to consider statistical power when achieving apparently "negative" results prevents accurate interpretation of the results. A nonsignificant result can be obtained when one includes an insufficient number of subjects to permit observation of a true effect (low power to detect an effect), or when one has an adequate number of subjects, but a meaningful effect does not exist (high power, no effect); one can also have a situation of lower power and no real effect. Without considering power, one is unable to distinguish a "negative" experiment from an inadequate one. This article examines 154 published nonsignificant t-test results. When power is calculated with an effect size equal to a standardized difference of unity, over 50% of the tests have inadequate power.
Pulver
A E
AE
University of Maryland School of Medicine, Maryland Psychiatric Research Center, Baltimore 21228.
Bartko
J J
JJ
McGrath
J A
JA
D002986:Clinical Trials as Topic; D006801:Humans; D011594:Psychometrics; D013223:Statistics as Topic