Erick H. Turner, MD
Potential Conflicts of Interest: Dr. Turner was on speakers' bureaus for AstraZeneca, Bristol-Myers Squibb, and Eli Lilly; these activities ceased 5 years ago.
Turner E.; The Effect of Funding Source on Outcome Reporting Among Drug Trials. Ann Intern Med. 2011;154:137. doi: 10.7326/0003-4819-154-2-201101180-00018
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Published: Ann Intern Med. 2011;154(2):137.
TO THE EDITOR:
I read Bourgeois and colleagues' recent article (1) with interest, and I agree with the point made in the rapid responses on www.annals.org about the importance of the differences in sample size. Although this confounding variable was not mentioned in the article's Discussion section, it could have played a major role in generating the outcome observed.
As can be seen in the authors' Table 1, the median final sample size for the industry-sponsored trials was 3 times larger than that for the trials funded by nonprofit or nonfederal organizations and 8 times larger than that for the government-sponsored trials. Let us assume that 3 hypothetical trials were performed on the same drug and the trials were identical in all respects except for sample size, such that each trial resulted in a “medium” effect size of 0.5 (one half of an SD) (2). Using the median final sample size of 191 for industry-sponsored trials, one calculates a highly “favorable” P value of 0.001. Using the median final sample size of 63 for the trials funded by nonprofit or nonfederal organizations, one calculates a P value of 0.05, which is at the threshold of statistical significance as typically defined. Using a sample size of 23 for the government-sponsored trials, one calculates a clearly “unfavorable” P value of 0.24, which represents a type II error.
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