Abstract
Interference tasks (e.g., the Stroop task) exhibit low test–retest reliability, which hinders the measurement of individual differences. This study examined whether controlling the interference rate improves reliability. The interference rate is a metric derived from the Horse-Race Model, defined as the probability of experiencing semantic-color conflict in incongruent Stroop trials (distinct from list-wide congruency, i.e., the proportion of incongruent trials in a block). In Studies 1a and 1b, interference rate was positively correlated with the magnitude of the Stroop effect, indicating that it accounts for meaningful individual variability. In Study 2, the fixed-interference-rate group (IR-fixed) had their interference rate controlled at 75% across two testing sessions (2-week interval) by adjusting the stimulus-onset asynchrony between semantic and color features (i.e., ensuring a 75% probability of experiencing interference in incongruent trials). Compared to the random-interference-rate group (IR-random), the IR-fixed group showed significantly higher test–retest reliability and stronger cross-session predictability of the Stroop effect, demonstrating that controlling the interference rate enhances measurement stability. Studies 1b and 2 also revealed moderate cross-session correlations for interference rate, regardless of whether the interval was a single Stroop task administration or 2 weeks. Furthermore, across all studies, interference rate exhibited poor internal consistency (McDonald’s ω < .60). Overall, the results suggest that interference rate can predict the Stroop effect but is not a stable psychological trait; instead, it fluctuates within a certain range. Therefore, failing to control the interference rate adversely impacts the test–retest reliability of the Stroop task.
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