Do Participants Differ in Their Cognitive Abilities, Task Motivation, or Personality Characteristics as a Function of Time of Participation?

Four experiments tested the conventional wisdom in experimental psychology that participants who complete laboratory tasks systematically differ in their cognitive abilities, motivational levels, and personality characteristics as a function of the time at which they participate during an academic term. Across 4 experiments with over 2,900 participants from 2 different universities with 2 different academic schedules, no convincing evidence suggested that individuals differ in cognitive abilities (working memory capacity, fluid intelligence, crystallized intelligence, long-term memory, and attention control). Similarly, no evidence suggested participants' task motivation varies systematically with time of participation, nor do any of the Big Five personality traits. The present study concludes that researchers need not be overly concerned with time of participation effects as a potential confound in individual differences or experimental psychology.