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Many studies in the psychological literature are underpowered (Bakker, van Dijk, & Wicherts, 2012; Cohen, 1990; Maxwell & Delaney, 2004). Specifically, in light of the typical effect sizes (ES) and sample sizes seen in the literature, typical power is estimated to be less than .50 (Cohen, 1990) or even .35 (Bakker et al., 2012). A recent study showed that the intuitions of researchers about power are also flawed, especially when ES are small to medium sized, and only half of the researchers use power analyses to make sample size decisions (Bakker, Hartgerink, Wicherts, & van der Maas, 2016). A possible solution is a formal power analysis which is reported a priori. Two ways to force researchers to make a formal power analysis before starting the experiment is to incorporate the power analysis in a preregistration or in an Institutional Review Board (IRB) proposal. In this study we will investigate whether the statistical power of a study is better when researchers are asked to make a formal power analysis before collecting the data.
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