When trials are carried out to assess the effectiveness of a drug, it is an important to have a control group of patients who are not given the drug. Neither the researchers nor the patients should know who is in the treatment group and who is in the control group. In other words they should be 'blinded'. There are different ways in which this blinding can be achieved. French researchers carefully studied all the reports of drug trials that involved blinding, published in the course of one year. They have produced a classification of the methods used.

The findings of the review should lead to a better understanding of different blinding methods and their effectiveness. This will help researchers design better trials in the future, and also help readers interpret the quality of trials. The authors of the review also say that blinding methods are often not described in enough detail in published scientific papers. They recommend that guidelines for the reporting of trials are improved.