# Carryover Effects (2 of 4)

Assume two experimental conditions: A1 and A2. Half the subjects perform in Condition A1 first and then in A2; the other subjects perform in Condition A2 first and then in A1. The following table of means shows "symmetric carryover effects."

 Condition Order A1 A2 A1 given first 8 A2 given first 5 A1 given second 10 A2 given second 7

First notice that performance in Condition A1 is three points better than performance in Condition A2. That is, performance was three points higher in A1 when A1 was first than it was in A2 when A2 was first. The same is true for performance in a condition when it was performed second.

Now consider the carryover effects by comparing the performance in Condition A1 when A1 was given first with performance in Condition A1 when A1 was given second. The table shows that performance in Condition A1 was two points better when it was given second (10) than when it was given first (8). Now, notice that the carryover effect is the same for Condition A2: Performance in A2 was two points better when it was performed second (7) than when it was performed first (5). Therefore, performing in Condition A1 prior to performing in Condition A2 raises performance in Condition A2 by two points. Analogously, performing in Condition A2 prior to performing in Condition A1 raises performance in Condition A1 by two points. The carryover effects are thus symmetric.