Abstract
Many randomized clinical trials fail to play out as intended: some participants assigned to the treatment group remain untreated, while others assigned to the control group cross over and receive treatment. In such settings, intention-to-treat analyses that compare participants by treatment assignment are diluted by noncompliance, while per-protocol analyses that compare participants by treatment received are contaminated by selection bias.
This talk explains how instrumental variables methods address both problems. The utility of instrumental variables methods in clinical trials is illustrated using two types of trials. The first, a "strategy trial", contrasts invasive and non-invasive treatments for patients with ischemic heart disease. The second, a set of "pragmatic trials", evaluates effects of cancer screening on cancer incidence. I argue that instrumental variables analysis should be central to pragmatic trials of all kinds, strategy trials in particular, and emerging nudge trials that encourage specific health-related behaviours in large populations.
