Reading focus
Syllabus: When Do Psychological Findings Generalize?
Connect the power illustration to the historical questionnaire example. The issue is both how precisely an effect is estimated and which materials the claim concerns.
Why you’re reading it. Recognize stimulus sampling as a design decision rather than a detail repaired by a larger participant sample.
A question to consider. Design a replication that includes original and new word lists. What comparison would reveal whether the finding depends on the original materials?
Why this reading
Recruiting more participants cannot resolve every uncertainty in an experiment. Westfall and colleagues show why a small set of words, faces or scenarios can limit both precision and the reach of a result.
Before you read
A stimulus is material presented to a participant. When the claim concerns a larger set of possible materials, differences between sampled stimuli matter. A random-effects model represents such variation; its usefulness depends on the sampling and modeling assumptions.
Read for
- Track why power can level off as participant numbers increase while the stimulus set stays fixed.
- Compare reusing, replacing and expanding the original materials. Use the risky-shift history to examine what repeated success with one questionnaire did not establish.
Consider afterwards
- You can add participants or add comparable scenarios to a replication. What information would determine which change improves the study more?
Editorial context
The argument concerns materials treated as samples from a wider domain. If the exact materials exhaust the intended target, the inference differs. The power illustration is model-based, and the historical example is a methodological case discussion. Neither supports a universal quota for stimuli.