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. 2008 Aug 26;5(8):e177.
doi: 10.1371/journal.pmed.0050177.

Mendelian randomisation and causal inference in observational epidemiology

Nuala A Sheehan  1 , Vanessa Didelez, Paul R Burton, Martin D Tobin
Affiliations

Mendelian randomisation and causal inference in observational epidemiology

Nuala A Sheehan et al. PLoS Med. .

Abstract

Nuala Sheehan and colleagues describe how Mendelian randomization provides an alternative way of dealing with the problems of observational studies, especially confounding.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. The ApoE Genotype as an Instrumental Variable in a Mendelian Randomisation Application
The arrows can be thought of as representing causal relationships, but this is not what matters here. What is essential is the absence of an arrow between ApoE and the confounders and between ApoE and cancer, as detailed in the three key assumptions in the text.
Figure 2
Figure 2. A Mendelian Randomisation Study Where the Chosen Instrument Is in Linkage Disequilibrium with a Variant Associated With, or Causal For, the Disease
Note that the direction of the arrow depicting the statistical association between the two genes is interchangeable.
Figure 3
Figure 3. A Mendelian Randomisation Study Where the Chosen Instrument Is in Linkage Disequilibrium with a Variant That Is Also Causal for the Intermediate Exposure
Figure 4
Figure 4. A Mendelian Randomisation Study Where the Chosen Instrument Is Not Directly Causal for the Exposure, But Is in Linkage Disequilibrium with Another Variant That Is
Figure 5
Figure 5. Maternal FTO Only Qualifies as an Instrument Conditional On Offspring FTO
See this image and copyright information in PMC

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