Blinding in Clinical Trials: Seeing the Big Picture

Abstract

Blinding mitigates several sources of bias which, if left unchecked, can quantitively affect study outcomes. Blinding remains under-utilized, particularly in non-pharmaceutical clinical trials, but is often highly feasible through simple measures. Although blinding is generally viewed as an effective method by which to eliminate bias, blinding does also pose some inherent limitations, and it behooves clinicians and researchers to be aware of such caveats. This article will review general principles for blinding in clinical trials, including examples of useful blinding techniques for both pharmaceutical and non-pharmaceutical trials, while also highlighting the limitations and potential consequences of blinding. Appropriate reporting on blinding in trial protocols and manuscripts, as well as future directions for blinding research, will also be discussed.

Keywords: bias; blinding; clinical trials; double; single; triple.

Figure 1

Sham procedure performed according to the category of treatment assessed. Reprinted with permission from ref. [43]. Copyright 2007 Boutron et al. Full text available from https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.0040061#s5.

Figure 2

Methods of blinding participants, health care providers, or other caregivers that rely on the category of treatment and comparator assessed. Reprinted with permission from ref. [43]. Copyright 2007 Boutron et al. Full text available from https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.0040061#s5.