The Limits of Direct Replications and the Virtues of Stimulus Sampling

While direct replications such as the ‘‘Many Labs’’ project are extremely valuable in testing the reliability of published findings across laboratories, they reflect the common reliance in psychology on single vignettes or stimuli, which limits the scope of the conclusions that can be reached. New experimental tools and statistical techniques make it easier to routinely sample stimuli, and to appropriately treat them as random factors. We encourage researchers to get into the habit of including multiple versions of the content (e.g., stimuli or vignettes) in their designs, to increase confidence in cross-stimulus generalization and to yield more realistic estimates of effect size. We call on editors to be aware of the challenges inherent in such stimulus sampling, to expect and tolerate unexplained variability in observed effect size between stimuli, and to encourage stimulus sampling instead of the deceptively cleaner picture offered by the current reliance on single stimuli.