Smoking cessation trials
========================

* Kristian B. Filion, MSc
* Patrick Bélisle, MSc
* Lawrence Joseph, PhD
* Gilles Paradis, MD MSc
* Stéphane Rinfret, MD MSc
* Mark J. Eisenberg, MD MPH

*   © 2008 Canadian Medical Association or its licensors

[Six of the authors respond:]

We thank John Polito for his discussion of the importance of blinding in clinical trials. Blinding is undoubtedly a key component of the validity of inferences drawn from randomized controlled trials. For this reason, it is included in tools to assess the quality of clinical trials, such as the Jadad scale.1 In our meta-analysis of randomized controlled trials of smoking cessation pharmacotherapies, we restricted our study to double-blind trials so that only trials of the highest quality would be included.2 We agree with Polito that maintaining blinding may be difficult, particularly if study participants experience withdrawal symptoms. However, although the importance of blinding is well established, assessing the integrity of blinding remains more controversial.

In a recent analysis of randomized controlled trials that reported tests for the success of blinding, Hróbjartsson and colleagues found that less than 2% of trials reported such testing.3 Others have reported this percentage to be as high as 8%.4 One reason few trial reports include tests for blinding is that it is unclear what these tests actually measure. Some have argued that such tests are often biased.5 These tests often do not test blinding but rather test the participant's or physician's belief regarding the efficacy of the treatment.6 Thus, the fact that patients who are randomly assigned to receive placebo and subsequently resume smoking correctly guess their allocated treatment may not be a reflection of the blinding itself but rather of their belief that the placebo is not efficacious.

Blinding plays an important role in ensuring the validity of clinical trial results. However, improved methods are needed to assess the success of blinding. Until such methods are developed, incomplete blinding is a potential limitation to most clinical trials.

## Footnotes

*   **Competing interests:** Mark Eisenberg is a member of the Varenicline Advisory Board of Pfizer Canada Inc. No competing interests declared by Kristian Filion, Patrick Bélisle, Lawrence Joseph, Gilles Paradis or Stéphane Rinfret.

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