Consistency in the time of experiment participation and personality correlates: a methodological note

Certain voluntary human participant pool procedures (e.g. where the participant selects when to participate in experiments) can compromise the representativeness of samples and the efficacy of random assignment procedures. In this study we recorded the time and date that university students participated in two experiments run during two different months in the same semester, and found significant test–retest correlations between times of participation. These correlations suggest that when students participate in psychological research may be a stable characteristic related to personality. We then correlated composite (combined across the two experiments) time and date scores with an array of standard demographic and personality measures, and found that experiment participation time was related to several personality variables (e.g. sensation seeking, morningness, achievement motivation). We conclude that, although the effect is likely to be small, some voluntary sign-up procedures and experimental procedures can introduce systematic bias in the form of personality differences.