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. 2010 Feb;63(2):154-62.
doi: 10.1016/j.jclinepi.2009.05.007. Epub 2009 Aug 27.

Trial sample size, but not trial quality, is associated with positive study outcome

Jasvinder A Singh  1 , Stephen Murphy, Mohit Bhandari
Affiliations

Trial sample size, but not trial quality, is associated with positive study outcome

Jasvinder A Singh et al. J Clin Epidemiol. 2010 Feb.

Abstract

Objective: To assess whether the reported trial quality or trial characteristics are associated with the trial outcome.

Study design and setting: We identified all eligible randomized controlled trials (RCTs) of arthroplasty from 1997 and 2006. Trials were classified based on whether the main trial outcome was reported to be positive (n = 90) or negative (n = 94). Multivariable logistic regression analyses studied the association of reporting of trial-quality measures (blinding, placebo use, allocation procedure, overall quality) and trial characteristics (intervention type, number of patients/centers, funding) with positive trial outcome.

Results: RCTs that used placebo or blinded care providers, used pharmacological interventions, had higher Jadad quality scores or sample size of more than 100 patients were significantly more likely to report positive result in univariate analyses. Multivariable regression did not identify methodological quality of RCTs, but rather found that sample size was associated with trial outcome. Studies with more than 100 patients were 2.2 times more likely to report a positive result than smaller studies (P = 0.04).

Conclusions: Lack of association of reported trial quality with positive outcome in multivariable analyses suggests that previously observed association of reported study quality with study outcome in univariate analyses may be mediated by other study characteristics, such as study sample size.

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Conflict of interest statement

Conflict Of Interest: None of the authors have any financial and personal relationships with other people or organizations that could inappropriately influence (bias) their work.

Figures

Figure 1
Figure 1. Flow chart of articles selected for review
aThe totals add up to more than these numbers, since many trials had both pharmacological and non-pharmacological interventions. b Many RCTs had more than one type of intervention, therefore the total adds up to a greater number. Positive nd negative RCTs were those that had the primary outcome reported as positive or negative, respectively. We excluded the 12 RCTs that reported the co-primary outcomes as one being positive and other being negative.
Figure 2
Figure 2. Association of overall trial quality with positive and negative results
See this image and copyright information in PMC

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