Meta-epidemiology and the MetaBLIND study: Response to Tack.

In 2020 we published MetaBLIND, a large meta-epidemiological study on the impact of masking on effect estimates in randomized clinical trials (RCTs). While masking is an established methodological practice in RCTs it is not clear to what extent results of non-masked RCTs are biased. Surprisingly, we found no evidence of an impact of masking on effect estimates, on average. Michiel Tack commented on the MetaBLIND study, and here we respond. The issues he raised were examples of standard themes when interpreting meta-epidemiological studies, which we have discussed at some length elsewhere, and did not warrant change of our conclusion. We maintain that the MetaBLIND results do not provide a sufficient basis for recommending abandoning masking as a methodological safeguard.