Asymmetric transfer (also known as asymmetric skill transfer) is a type of interference that occurs in a within subjects or repeated measures experiment. Interference occurs when the learning of new information or behaviors interacts with previous learning or memories and interferes with the acquisition of the new information. Treatment effects can be the result of the order in which the treatment was administered. This can cause a drug or treatment to appear to be either more effective or less effective than it actually is. A previous treatment may affect the placebo effect in participants.
Asymmetric transfer between conditions is surmised to be more common than is generally acknowledged. Some of the possible causes of asymmetric transfer are believed to be state dependent learning, not enough time lapsing between treatments, and the acquisition of learning techniques. Counterbalancing can be used as a means of avoiding asymmetric transfer. When counterbalancing is used to assign levels of a condition to participants to avoid asymmetric transfer it must be verified that the effect actually occurred - this is usually accomplished by using a statistical test like an analysis of variance. When doing this the researchers want there to be an insignificant group effect.
When the group effect is statistically significant then asymmetric transfer has occurred and counterbalancing did not work. If there is a likelihood that asymmetric transfer will occur, then a between-subjects design is probably the better option.