The Folly of Powering Replications Based on Observed Effect Size

Uri Simonsohn on replications:

It is common for researchers running replications to set their sample size assuming the effect size the original researchers got is correct. So if the original study found an effect-size of d=.73, the replicator assumes the true effect is d=.73, and sets sample size so as to have 90% chance, say, of getting a significant result. This apparently sensible way to power replications is actually deeply misleading.

Why misleading?

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