化学中讲的携带效应（Carry-over effect

化学中讲的携带效应（Carry-over effect

What are carry-over effects?A carryover effect is an effect that "carries over" from one experimental condition to another.Whenever subjects perform in more than one condition (as they do in within-subject designs) there is a possibility of carryover effects.For example,consider an experiment on the effect of rate of presentation on memory.Subjects are presented with a list of words and asked to recall as many words as they can.In one condition,the words are presented one word per second; in the other condition,the words are presented two words per second.The question is whether or not having performed in one condition affects performance in the second condition.Perhaps learning the first list of words will interfere with learning the second list because it will be hard to remember which words were in each list.Or maybe the practice involved learning one list will make it easier to learn a second list.In either case,there would be a carryover effect:performance on the second list would be affected by the experience of being given the first list.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."