MetaBLIND is the largest meta-epidemiological study on the impact of blinding in randomized trials to date. We examined MetaBLIND data on the impact of blinding patients on patient-reported outcomes. 68 out of 132 included trials tested knowledge recall and had questionable relevance to clinical trials. In 17 out of 18 comparisons, the number of trials in the blinded or nonblinded group was 2 or lower. In several key trials, the blinding status was uncertain. Effect sizes compared in MetaBLIND appear to reflect random differences in study design and setting rather than the impact of blinding trial participants.
Keywords: MetaBLIND; bias; blinding; meta-analysis; meta-epidemiological study.