Asymmetrical transfer: an inherent weakness of repeated-measure drug experiments.
When subjects act as their own controls in drug experiments there is a risk of asymmetrical transfer between treatment conditions, with the result that treatment effects are determined largely by order of administration. In such cases the effect of a drug may be reduced or exaggerated, and prior treatment with a drug may affect placebo conditions. Asymmetrical transfer is probably much more common than is generally realized. Suggested causes include inadequate wash-out between treatments, state-dependent learning, adoption of learning strategies, and practice effects. The problem is illustrated by the reanalysis of a paper on the effects of benzhexol on memory, published recently in this journal (Potamianos and Kellet, 1982). The advantages of separate-group experimental design are reconsidered.
D000368:Aged; D000704:Analysis of Variance; D006801:Humans; D007858:Learning; D008568:Memory / Q000187:drug effects*; D011939:Mental Recall / Q000187:drug effects; D012107:Research Design; D014282:Trihexyphenidyl / Q000008:administration & dosage / Q000494:pharmacology*; D014936:Word Association Tests
D014282:Trihexyphenidyl