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Drug Alcohol Rev. 2010 Mar;29(2):193-201. doi: 10.1111/j.1465-3362.2009.00096.x.

Ineligibility and refusal to participate in randomised trials of treatments for drug dependence.

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Institute of Health Management and Health Economics/HERO, University of Oslo, Blindern, Oslo, Norway.



The aim of this study is to examine the extent to which drug-dependent patients are ineligible for or unwilling to participate in randomised clinical trials. This is important because unrepresentative sample selection is a potentially important problem for randomised trials in the drug dependence field and little is known about the magnitude of the problem.


A total of 98 clinical trials were drawn for analysis from a systematic review of the drug dependence treatment literature.


The trials reviewed excluded an average of 29% of potential subjects as ineligible; a further 29% of the eligible subjects were unwilling to participate. Trials comparing widely different treatments had a higher proportion of ineligible and unwilling subjects than did studies comparing more similar treatments. Experiments with large samples enrolled a smaller proportion of patients from their sampling pool than did experiments with small samples.


Drug-dependent trial subjects are a minority of all drug patients seen in real-world clinical practice. It is necessary to improve the reporting of these potential problems in randomised trials. Systematic reviews of the literature ought to use this information to distinguish reliable from less reliable findings.


Unrepresentative sample selection is a serious problem for randomised trials in the drug dependence field.

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