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<p>The goal of this project is to examine whether repeated participation in a set of cognitive experiments affects the effect size found in these experiments. Chandler and colleagues (in press) found that repeated participation can reduce effect sizes. In their sample of 12 expriments, they observed a 25% reduction of effect sizes between testing wave 1 and testing wave 2. </p> <p>The experiments conducted by Chandler et al. were all in the realm of judgment and decision making, which typically rely on participants’ conscious processing. Participating in such studies can result in memories that might be recalled in subsequent participations and affect participants’ behavior (e.g., because the hypothesis becomes more transparent, or because previously acquired information affect people’s assessments). However, in the experiments to be tested in this project, the manipulation is typically quite subtle and relies on automatic processing. This would lead to the prediction that our effect sizes are not as susceptible to repeated testing as are judgment and decision-making experiments. More specifically, it leads to the prediction that effect size will not vary as a function of testing wave. In other words, the change in effect size will be close to zero.</p> <p>According to an alternative view, whether a task taps controlled vs. automatic processes does not impact the wave 2 effect size. What matters is that subjects have been exposed to the task before. This view predicts reduction in effect size comparable to the 25% found by Chandler et al.</p> <p>Bayesian analysis will be used to determine whether the effect size difference between waves 1 and 2 better fits a 0% reduction model or a 25% reduction model. </p> <p>Half the subjects saw the exact same version of the experiment in wave 2 whereas the other half received the same task but different stimuli. This manipulation allowed us to investigate whether the repetition of surface features of the experiment impacts the effect size in wave 2. According to the first view outlined above, the effect size will not be impacted by repetition. This means that changing surface features of the experiment will also not lead to a decrease in effect size relative to wave 1. If true, this would suggest that changing surface features of an experiment is unlikely to appreciably change its effect size compared to using a copy of the original experiment.</p> <p>According to the alternative view mentioned earlier, prior exposure to an experiment reduces the effect size. If the second exposure is to a variation of the experiment rather than to the same experiment, a smaller reduction in effect size might be expected, as subjects have previously been exposed to the experimental task during wave 1 but not to the stimuli.</p> <p>Reference</p> <p>Chandler, J., Paolacci, G., Peer, E., Mueller, P. & Ratliff, K.A. (2015). Using nonnaive participants can reduce effect sizes. <em>Psychological Science</em>, Accepted. doi: <a href="http://dx.doi.org/10.1177/0956797615585115" rel="nofollow">http://dx.doi.org/10.1177/0956797615585115</a></p>
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