Problems with Publishing Results of Interim Analyses of Randomized Clinical Trials

Law, Matthew G. PhD

National Centre in HIV Epidemiology and Clinical Research, The University of New South Wales, Darlinghurst, Australia

For correspondence or reprints contact: Matthew G. Law, PhD, National Centre in HIV Epidemiology and Clinical Research, The University of New South Wales, 376 Victoria Street, DARLINGHURST NSW 2010, Australia.

HIV Clinical Trials 1(3):p 30-36, November-December 2000.

Purpose:

This purpose of this study was to illustrate how publication of interim analyses of randomized clinical trials (RCTs) can cause problems in the interpretation of final results.

Method:

The effect of publishing interim analyses on the results of a typical HIV RCT comparing regimens of registered antiretroviral drugs was illustrated using a simulation study. Simulations modeled an RCT comparing the effect of two treatment combinations on changes in log HIV viral load from baseline. Publication of interim results at 6 months was assumed to lead to 50% of patients switching from the poorer treatment if interim results were statistically significant (p < .05), 20% of patients switching from the poorer treatment if interim results were marginally significant (.05 < p < .20), and 10% of all patients switching treatment if interim results were not statistically significant. Three scenarios were simulated: a large treatment difference (0.4 log HIV viral load), a moderate difference (0.2 log), and no treatment difference (0.0 log).

Results:

The simulation study showed that if the true treatment difference was large (0.4 log) the power of the trial was reduced from over 80% at 6 months to under 37% at 12 months. Furthermore, given the statistical significance of the interim analysis results at 6 months, the simulations illustrated that the trial results would appear similar at 12 months, regardless of the true underlying treatment difference.

Conclusion:

The simulations reinforce the fact that publication of interim analyses of RCTs can affect the future conduct of a trial and make interpretation of final results difficult.