Prevalence and factors associated with use of placebo control groups in randomized controlled trials in psoriasis: a cross-sectional study.
BACKGROUND
The ethics and science of using placebo control groups in clinical trials have been widely debated. Few studies, however, have examined factors associated with choice of control group.


OBJECTIVE
Our aim was to assess the prevalence of use of placebo controls in randomized controlled trials in psoriasis and to identify factors associated with use of placebo controls in these trials.


METHODS
This is a cross-sectional study of randomized controlled trials in psoriasis published from January 1, 2001 to December 20, 2005 and indexed in the Cochrane Central Register of Controlled Trials. We extracted data on types of control groups used, design issues (number of patients enrolled, primary end point), disease characteristics (psoriasis type and severity), and extrascientific issues (trial location, funding source, and year of publication). We used bivariable and multivariable logistic regression to determine factors associated with use of a placebo control group.


RESULTS
Of 194 citations, 187 were available for review. One hundred thirty-five trials from 134 articles in 38 journals met inclusion criteria. Eighty-three trials (61.5%) enrolling 8171 subjects (41.7%) used active controls only, and 52 trials (38.5%) enrolling 11,406 subjects (58.3%) used placebo controls. Adjusted for trial location and funding source, trials significantly more likely to have used placebo controls included those conducted in the United States (odds ratio [OR], 5.79; 95% confidence interval [CI], 2.45-13.68; P < .001) and those funded by pharmaceutical companies (OR, 2.61; 95% CI, 1.19-5.73; P = .02). Predicted frequencies of placebo use ranged from 77.6% (industry-funded, conducted trials in the United States) to 18.6% (non-industry-funded trials not conducted in the United States).


CONCLUSIONS
Our searches may not have identified all published trials, and we did not have access to data from unpublished trials.


CONCLUSIONS
Use of placebo controls has been more common in psoriasis trials conducted in the United States and funded by pharmaceutical companies. The findings suggest that ethical and scientific issues related to choice of control group in psoriasis trials are interpreted markedly differently depending on trial location and funding source.
Katz
Kenneth A
KA
Department of Dermatology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
Karlawish
Jason H
JH
Chiang
David S
DS
Bognet
Rachel A
RA
Propert
Katherine J
KJ
Margolis
David J
DJ
D003430:Cross-Sectional Studies; D004345:Drug Industry; D006801:Humans; D010919:Placebos; D011565:Psoriasis / Q000188:drug therapy*; D016032:Randomized Controlled Trials as Topic / Q000379:methods* / Q000706:statistics & numerical data; D012109:Research Support as Topic; D014481:United States
D010919:Placebos