Transcription of Tutorial Gpower - Statpower
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Tutorial Gpower - Statpower
Gpower Tutorial Before we begin this Tutorial , we would like to give you a general advice for performing power analyses. A very frequent error in performing power analyses with G*Power is to specify incorrect degrees of freedom. As a general rule, therefore, we recommend that you routinely compare the degrees of freedom as specified in G*Power with the degrees of freedom that your statistical analysis program gives you for an appropriate set of data. If you do not yet have your data set ( , in the case of an a priori power analysis), then you could simply create an appropriate artificial data set and check the degrees of freedom for this set. Let us now start with the simplest possible case, a t-test for independent samples. In a now-classic study, Warrington and Weiskrantz (1970) compared the memory performance of amnesics to normal controls.
Critical t: t(10) = 2.2281 Delta: 0.8165 This result is devastating: The relevant statistical test had virtually no power to detect a "medium" size difference between amnesics and controls in the word stem completion task. If we were to repeat the Warrington …
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