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Comment & Response
February 2018

Biased Estimates in Mendelian Randomization Studies Conducted in Unrepresentative Samples

Author Affiliations
  • 1MRC Integrative Epidemiology Unit, University of Bristol, Bristol, United Kingdom
  • 2UK Centre for Tobacco and Alcohol Studies, School of Experimental Psychology, University of Bristol, Bristol, United Kingdom
  • 3School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom
JAMA Cardiol. 2018;3(2):181. doi:10.1001/jamacardio.2017.4279

To the Editor Large cohort studies have transformed our ability to evaluate complex exposure-outcome relationships. However, these studies are typically not representative of the source population from which they are sampled because of selection at recruitment, attrition over time (in prospective studies), or both. For example, in UK Biobank, the response rate was approximately 5%, and the resulting sample was healthier and more highly educated than the general population of the United Kingdom.1