Assuring That Double-Blind Is Blind — Perlis et al. 167 (3): 250 — Am J Psychiatry

This article is  technical but very important.  To “double-blind” means to set up a clinical trial so neither the researchers or the patients know whether a patient is taking the actual drug being tested or the placebo.  The purpose of double blinding is to “ensure” objectivity.

This article points out a number of ways that a trial becomes accidentally unblinded (either the researchers or the subject figure out whether they are getting the actual drug or not.)

As a extra, be sure to click on the link and check out the conflict of interest disclosure at the end of the article.  It is wonderously long.  Btw, in this instance, I feel the authors have written a very good article despite the long disclosure statement.

“The gold standard for evidence in psychiatry, as elsewhere in medicine, is often considered to be the randomized, placebo-controlled, double-blind study. The use of blinding or masking plays a key role in these designs by addressing the problem of expectancy. First, if participants anticipate greater benefit from a particular treatment, they may be more likely to respond to it, which is considered a component of placebo response. Not surprisingly, participants have been found to report greater anticipated benefits when they were randomized to enter an active-comparator, versus a placebo-comparator, study (1). Likewise, raters may anticipate greater benefit from active drug and thus favor it in their ratings, whether consciously or unconsciously. Greater response rates in both active and placebo arms occur when a greater proportion of participants receive active treatment—that is, when patients (1) or raters (2) expect more participants to benefit.

Double-blinding, typically by providing drug and placebo in identical capsules, is intended to minimize the impact of expectancy and the related concept of credibility. The blind may be compromised in a variety of ways, however, beginning with differences in medication taste or smell. Of particular concern may be the emergence of adverse effects, particularly when those adverse effects are known to be associated with a specific medication. The requirement that informed consent forms delineate common adverse effects may increase this risk (3). Indeed, when the degree of unblinding is assessed in antidepressant trials, multiple reports suggest that it is extensive: at least three-quarters of patients are typically able to correctly guess at their treatment assignment (4, 5). Moreover, even the sudden absence of adverse effects may contribute to unblinding, as might occur when a participant stabilized on a sedating medication is abruptly switched to placebo at randomization in a relapse-prevention study…. much more at the link

via Assuring That Double-Blind Is Blind — Perlis et al. 167 (3): 250 — Am J Psychiatry.

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