Meta-analyses of Randomized Controlled Trials

Abstract

Double-blind placebo-controlled trials control for many types of biases, including selection bias, confounding, placebo effects, time effects, carryover effects, interactions etc. Are they, therefore, necessarily perfect? In this chapter eight reasons are given why this is not so. It is, nonetheless, a very interesting and generally very rewarding activity as we shall see. Three recently published meta-analyses from the authors are used as examples. The first meta-analysis showed robustness against the differences between parallel-group and crossover designs. The second showed that multiple outcome variables were helpful in many ways to answer the overall scientific question. The third showed that large meta-analyses of randomized controlled trials need not necessarily be tested for pitfall assessment.