Shadish W R, Ragsdale K
Department of Psychology, University of Memphis, Tennessee 38152, USA.
J Consult Clin Psychol. 1996 Dec;64(6):1290-305.
Psychotherapy meta-analyses commonly combine results from controlled experiments that use random and nonrandom assignment without examining whether the 2 methods give the same answer. Results from this article call this practice into question. With the use of outcome studies of marital and family therapy, 64 experiments using random assignment yielded consistently higher mean post-test effects and less variable posttest effects than 36 studies using nonrandom assignment. This difference was reduced by about half by taking into account various covariates, especially pretest effect size levels and various characteristics of control groups. The importance of this finding depends on (a) whether one is discussing meta-analysis or primary experiments, (b) how precise an answer is desired, and (c) whether some adjustment to the data from studies using nonrandom assignment is possible. It is concluded that studies using nonrandom assignment may produce acceptable approximations to results from randomized experiments under some circumstances but that reliance on results from randomized experiments as the gold standard is still well founded.
心理治疗的元分析通常会合并来自使用随机和非随机分配的对照实验的结果，而不考察这两种方法是否会得出相同的答案。本文的研究结果对这种做法提出了质疑。通过对婚姻和家庭治疗的结果研究发现，与36项使用非随机分配的研究相比，64项使用随机分配的实验在测试后的平均效应始终更高，且测试后的效应变化更小。通过考虑各种协变量，尤其是测试前的效应量水平和对照组的各种特征，这种差异减少了约一半。这一发现的重要性取决于：（a）讨论的是元分析还是初级实验；（b）期望答案有多精确；（c）是否有可能对使用非随机分配的研究数据进行某种调整。得出的结论是，在某些情况下，使用非随机分配的研究可能会产生与随机实验结果可接受的近似值，但将随机实验结果作为金标准仍然是有充分依据的。
