Reporting Methods of Blinding in Randomized Trials Assessing Nonpharmacological Treatments

Abstract

Background

Blinding is a cornerstone of treatment evaluation. Blinding is more difficult to obtain in trials assessing nonpharmacological treatment and frequently relies on “creative” (nonstandard) methods. The purpose of this study was to systematically describe the strategies used to obtain blinding in a sample of randomized controlled trials of nonpharmacological treatment.

Methods and Findings

We systematically searched in Medline and the Cochrane Methodology Register for randomized controlled trials (RCTs) assessing nonpharmacological treatment with blinding, published during 2004 in high-impact-factor journals. Data were extracted using a standardized extraction form. We identified 145 articles, with the method of blinding described in 123 of the reports. Methods of blinding of participants and/or health care providers and/or other caregivers concerned mainly use of sham procedures such as simulation of surgical procedures, similar attention-control interventions, or a placebo with a different mode of administration for rehabilitation or psychotherapy. Trials assessing devices reported various placebo interventions such as use of sham prosthesis, identical apparatus (e.g., identical but inactivated machine or use of activated machine with a barrier to block the treatment), or simulation of using a device. Blinding participants to the study hypothesis was also an important method of blinding. The methods reported for blinding outcome assessors relied mainly on centralized assessment of paraclinical examinations, clinical examinations (i.e., use of video, audiotape, photography), or adjudications of clinical events.

Conclusions

This study classifies blinding methods and provides a detailed description of methods that could overcome some barriers of blinding in clinical trials assessing nonpharmacological treatment, and provides information for readers assessing the quality of results of such trials.

Abstract

An assessment of blinding methods used in nonpharmacological trials published in one year in high-impact factor journals classifies methods used and describes methods that could overcome some barriers of blinding.

Editors' Summary

Background.

Well-conducted “randomized controlled trials” are generally considered to be the most reliable source of information about the effects of medical treatments. In a randomized trial, the play of chance is used to decide whether each patient receives the treatment under investigation, or whether he/she is assigned to a “control” group receiving the standard treatment for their condition. This helps makes sure that the two groups of patients receiving the different treatments are equivalent at the start of the trial. Proper randomization also prevents doctors from deciding which treatment individual patients are given, which could distort the results. An additional technique used is “blinding,” which involves taking steps to prevent patients, doctors, or other people involved in the trial (e.g., those recording measurements) from finding out which patients have received which treatment. Properly done, blinding should make sure the results of a trial are more accurate. This is because in an unblinded study, participants may respond better if they know they have received a promising new treatment (or worse if they only got a placebo or an old drug). In addition, doctors and others in the research team may “want” a particular treatment to perform better in the trial, and unthinking bias could creep into their measurements or actions. However, blinding is not a simple, single step; the people carrying out the trial often have to set up a variety of different procedures.

Why Was This Study Done?

The authors of this study had already conducted research into the way in which blinding is done in trials involving drug (“pharmacological”) treatment. Their work was published in October 2006 in PLoS Medicine. However, concealing from patients the type of pill that they are being given is much easier than, for example, concealing whether or not they are having surgery or whether or not they are having psychotherapy. The authors therefore set out to look at the methods that are in use for blinding in nonpharmacological trials. They hoped that a better understanding of the different blinding methods would help people doing trials to design better trials in the future, and also help readers to interpret the quality of completed trials.

What Did the Researchers Do and Find?

The authors systematically searched the published medical literature to find all randomized, blinded drug trials published in just one year (2004) in a number of different “high-impact” journals (well-regarded journals whose articles are often mentioned in other articles). Then, they classified information from the published trial reports. They ended up with 145 trial reports, of which 123 described how blinding was done. The trials covered a wide range of medical conditions and types of treatment. The blinding methods used mainly involved the use of “sham” procedures. Thus, in 80% of the studies in which the treatment involved a medical device, a pretend device had been used to make patients in the control group think they were receiving treatment. In many of the treatments involving surgery, researchers had devised elaborate ways of making patients think they had had an operation. When the treatment involved manipulation (e.g. physiotherapy or chiropractic), fake “hands-on” techniques were given to the control patients. The authors of this systematic review classify all the other techniques that were used to blind both the patients and members of the research teams. They found that some highly innovative ideas have been successfully put into practice.

What Do These Findings Mean?

The authors have provided a detailed description of methods that could overcome some barriers of blinding in clinical trials assessing nonpharmacological treatment. The classification of the techniques used will be useful for other researchers considering what sort of blinding they will use in their own research.

Additional Information.

Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040061.

• The James Lind Library has been created to help patients and researchers understand fair tests of treatments in health care by illustrating how fair tests have developed over the centuries

• ClinicalTrials.gov, a trial registry created by the US National Institutes of Health, has an introduction to understanding clinical trials

• The UK National Health Service National Electronic Library for Health has an introduction to controlled clinical trials

• The CONSORT statement is intended to strengthen evidence-based reporting of clinical trials