Journal
EUROPEAN JOURNAL OF EPIDEMIOLOGY
Volume 32, Issue 5, Pages 377-389Publisher
SPRINGER
DOI: 10.1007/s10654-017-0255-x
Keywords
Mendelian randomization; Instrumental variable; Robust methods; MR-Egger; Summarized data
Categories
Funding
- Sir Henry Dale Fellowship - Wellcome Trust [204623/Z/16/Z]
- Sir Henry Dale Fellowship - Royal Society [204623/Z/16/Z]
- British Heart Foundation [CH/12/2/29428]
- MRC [MC_UU_00002/7, MC_UP_0801/1, G0700463, MR/L003120/1] Funding Source: UKRI
- British Heart Foundation [RG/08/014/24067, CH/12/2/29428] Funding Source: researchfish
- Medical Research Council [MC_UU_00002/7, G0700463, MC_UP_0801/1, MR/L003120/1] Funding Source: researchfish
- National Institute for Health Research [NF-SI-0512-10165] Funding Source: researchfish
- Wellcome Trust [204623/Z/16/Z] Funding Source: researchfish
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Mendelian randomization-Egger (MR-Egger) is an analysis method for Mendelian randomization using summarized genetic data. MR-Egger consists of three parts: (1) a test for directional pleiotropy, (2) a test for a causal effect, and (3) an estimate of the causal effect. While conventional analysis methods for Mendelian randomization assume that all genetic variants satisfy the instrumental variable assumptions, the MR-Egger method is able to assess whether genetic variants have pleiotropic effects on the outcome that differ on average from zero (directional pleiotropy), as well as to provide a consistent estimate of the causal effect, under a weaker assumption-the InSIDE (INstrument Strength Independent of Direct Effect) assumption. In this paper, we provide a critical assessment of the MR-Egger method with regard to its implementation and interpretation. While the MR-Egger method is a worthwhile sensitivity analysis for detecting violations of the instrumental variable assumptions, there are several reasons why causal estimates from the MR-Egger method may be biased and have inflated Type 1 error rates in practice, including violations of the InSIDE assumption and the influence of outlying variants. The issues raised in this paper have potentially serious consequences for causal inferences from the MR-Egger approach. We give examples of scenarios in which the estimates from conventional Mendelian randomization methods and MR-Egger differ, and discuss how to interpret findings in such cases.
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