Diary studies die from attrition. Participants stop submitting entries, quality degrades, and your data collapses. Nielsen Norman Group identifies the incentive structure as the single strongest lever researchers have against this failure mode.
The core mechanic is different from standard UX research: moderated sessions pay for time, diary studies pay for effort. That shift changes everything. Tie compensation to submission quantity and quality, or participants will game the threshold, batch entries at the last minute, or submit low-effort responses just to qualify for payment.
The full article is worth reading for its specific structural recommendations, not just the principle. If you run studies longer than two weeks, the design of your incentive schedule is probably your biggest methodological risk, and this piece treats it with the precision that risk deserves.
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