Monday, August 20, 2012

Clinical trials: enrollment targets vs. valid hypothesis testing

The questions raised in this Scientific American article ought to concern all of us, and I want to take some of these questions further. But let me first explain the problem.

Clinical trials and observational studies of drugs, biologics, and medical devices are a huge logistical challenge, not the least of which is finding physicians and patients to participate. The thesis of the article is that the classical methods of finding participants – mostly compensation – lead to perverse incentives to lie about one’s medical condition.

I think there is a more subtle issue, and it struck me when one of our clinical people expressed a desire not to put enrollment caps on large hospitals for the sake of a fast enrollment. In our race to finish the trial and collect data, we are biasing our studies toward larger centers where there may be better care. This effect is exactly the opposite of that posited in the article, where treatment effect is biased downward. Here, treatment effect is biased upward, with doctors more familiar with best delivery practices (many of the drugs I study are IV or hospital-based), best treatment practices, and more efficient care.

We statisticians can start to characterize the problem by looking at treatment effect by different sites, or using hierarchical models to separate out center effect from drug. But this isn’t always a great solution, because low-enrolling sites, by definition, have a lot fewer people, and pooling is problematic because low-enrolling centers tend to have way more variation in level and quality of care than high-enrolling centers.

We can get creative on the statistical analysis end of studies, but I think the best solution is going to involve stepping back at the clinical trial logistics planning stage and recasting the recruitment problem in terms of a generalizability/speed tradeoff.