Healthy Skepticism Library item: 8001

Warning: This library includes all items relevant to health product marketing that we are aware of regardless of quality. Often we do not agree with all or part of the contents.

Publication type: Journal Article

Editors.
Observational studies should carry a health warning
BMJ 2007 Jan 27; 334:(7586):179
http://www.bmj.com/cgi/content/full/334/7586/179-c

Abstract:

Observational studies have their place, although the results often depend crucially on the type of analysis used to generate them. A good illustration of this principle comes from a study comparing four different ways of looking at the effects of invasive revascularisation after heart attack. Essentially, all four methods adjusted for the many baseline differences between people who have invasive treatments and people who don’t, differences that would normally be eliminated by randomisation in a randomised trial.

Using data from 73 238 Medicare patients, the authors showed that standard analytical methods-multivariate risk adjustment and two methods based on propensity scoring-came up with a survival benefit of around 50% (adjusted relative risks 0.51, 0.54, and 0.54). A newer method called instrumental variable analysis indicated a more modest survival benefit of 16% (adjusted relative risk 0.84), closer to the results from randomised trials. Does the new analysis get nearer “the truth” than . . .