The response time-based concealed information test can reveal when a person recognizes a relevant item among other, irrelevant items, based on comparatively slower responding. Thereby, if a person is concealing the knowledge about the relevance of this item (e.g., recognizing it as a murder weapon), this deception can be revealed. A recent study, conducted online and using a between-subject design, introduced a significantly enhanced version by including additional items in the task. While this modified version outperformed the original version, it also resulted in a much higher rate of participant dropouts (i.e., participants leaving the experiment's website without completing the task). The grave implication is that the perceived enhancement is perhaps merely due to selective attrition. Therefore, the current experiment replicates the original one, but using a within-subject design. The results show that there is a large enhancement even when selective attrition is prevented.