Optional stopping does not bias parameter estimates (if done correctly)

(This article was originally published at Nicebread, and syndicated at StatsBlogs.)

tl;dr: Optional stopping does not bias parameter estimates from a frequentist point of view if all studies are reported (i.e., no publication bias exists) and effect sizes are appropriately meta-analytically weighted. Several recent discussions on the Psychological Methods Facebook group surrounded the question whether an optional stopping procedure leads to biased effect size estimates (see […]

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