Larissa Govers, BSc
When you want to study the effect of a therapeutic intervention, randomisation is the most reliable method to assess the real effect of the intervention. Randomisation is the process of assigning participants or experimental units to a certain treatment in a way that every unit has a known (equal) chance of being assigned to any of the groups. However, the results from these studies could still be biased due to systematic differences. Already from early on in our (bio)medical studies, we got taught that blinding is very important in order to conduct good science and to decrease the risk of bias. To study this, researchers found that, on average, randomised trials that had not been blinded properly showed larger treatment effects than well-blinded studies .
However, recently a paper got published defying all that we have learned: they found that there actually is no difference in the estimated treatment effect between trials with and without blinded patients, healthcare providers and outcome assessors . But how could they study this? They made a meta-analysis of all the meta-analyses that are out there, which study the effect of blinding. This is a good way to increase the power and the reliability of the study because 142 meta-analyses (1153 trials) were included in the data. Analysing these trials, they found that the type of comparator (e.g. active comparator) did not seem to affect the analyses. However, they did not explore the impact of blinding on different types of analyses. To strengthen their statement, other systematic reviews also found that blinding has surprisingly little effect on the outcome .
What we can take away from this paper is that blinding is less vital than we get taught to believe. Therefore, for the future of clinical trials, it will be essential to assess in what circumstances blinding is important and how to determine the risk of bias.
 Day SJ, Altman DG. Statistics notes: blinding in clinical trials and other studies. BMJ. 2000;321(7259):504.
 Moustgaard H, Clayton GL, Jones HE, Boutron I, Jorgensen L, Laursen DRT, et al. Impact of blinding on estimated treatment effects in randomised clinical trials: meta-epidemiological study. BMJ. 2020;368:l6802.
 Page MJ, Higgins JP, Clayton G, Sterne JA, Hrobjartsson A, Savovic J. Empirical Evidence of Study Design Biases in Randomized Trials: Systematic Review of Meta-Epidemiological Studies. PLoS One. 2016;11(7):e0159267.