**Objective** Standardized face-to-face interviews are widely used to collect data in low and middle-income countries for social science and health research. Such interviews can be long and tedious. In an attempt to improve the respondents’ experience during interviews, we developed a concept of gamified interview by including a game element. Gamification is reported to increase engagement in tasks, but results from rigorously developed research are equivocal, and a theory of gamification is still needed. **Materials & methods** We conducted a randomized controlled trial to rigorously evaluate the proposed gamification based on the self-determination theory, specifically on the basic psychological needs theory. In total, 1266 respondents were interviewed. Single and multiple mediation analyses were used to understand how gamification works. **Results** Our evaluation showed that the gamification we had developed did not improve the outcome, i.e. the reported experience of the interview. The effect of gamification depended on the ability of respondents: gamification can be counterproductive if it overburdens the respondents. Finally, the basic psychological needs theory explained the mechanisms of action of gamification well: feeling competent and related to others improved the reported experience of the interview. **Conclusion** We emphasize the need to develop context-specific gamification and invite researchers to follow equivalently rigorous evaluation of gamification in future studies.
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