Research Article: Reporting Methods of Blinding in Randomized Trials Assessing Nonpharmacological Treatments

Date Published: February 20, 2007

Publisher: Public Library of Science

Author(s): Isabelle Boutron, Lydia Guittet, Candice Estellat, David Moher, Asbjørn Hróbjartsson, Philippe Ravaud, Ian Ford

Abstract: BackgroundBlinding 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 FindingsWe 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.ConclusionsThis 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.

Partial Text: Bias in clinical research can be described as systematic error that can result in false treatment effect estimates [1]. Bias may cause a investigators to misinterpret the result of any research finding. Randomized controlled trials (RCTs) are widely recognized as being the best design for avoiding and/or minimizing bias. Blinding, although not possible in every study, is an important methodological technique to help reduce the influence bias may have on the results of an evaluation [2–9]. Blinding refers to keeping key persons, such as participants, health care providers, and outcome assessors, unaware of the treatment administered or of the true hypothesis of the trial [3,5,6]. Blinding of participants and health care providers prevents performance bias that occurs if additional therapeutic interventions (i.e., cointerventions) are provided preferentially in one of the comparison groups [10]. Blinding of outcome assessors minimizes the risk of detection bias (i.e., observer, ascertainment, assessment bias). This type of bias occurs if participant assignment influences the process of outcome assessment [10]. For example, nonblinded neurologists assessing the outcome from a trial [9] demonstrated an apparent treatment benefit, whereas blinded neurologists did not. Finally, blinding of data analysts can also prevent bias, as knowledge of the intervention received may influence the choice of analytical strategies and methods [10]. Empirical evidence has demonstrated that lack of reporting of double blinding is responsible for biased treatment estimates [1,2,11–13].

This study provides a detailed description and classification, with examples of reporting, of different methods of blinding participants, health care providers or other caregivers, and outcome assessors in a large series of RCTs assessing NPT. Our results highlight innovative methods of blinding and allow for a description of possible placebos for NPT in trials.



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