Evidence map›Paper›PMID 33527565›Full record

ArticleGenetic epidemiology2021

Mendelian randomisation with coarsened exposures.

Matthew J Tudball, Jack Bowden, Rachael A Hughes, Amanda Ly, Marcus R Munafò, Kate Tilling, Qingyuan Zhao, George Davey Smith

Abstract read
In one paragraph

Article in Genetic epidemiology, 2021. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 17 papers.

0numbers the graph read from it
0cells of the map it votes in
17citing papers in PubMed
–field-weighted citation impact
1 · What the graph read from it

What it found

Each row is one number read from the abstract, on the scale the paper reported it, with its interval. Left of the dashed line favours the treatment, right favours the comparator. Under each row is the sentence it came from. New to these charts? A ten-minute tutorial.

The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.

2 · The registry

The trial behind it

Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.

Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.

3 · Its place in the literature

Who cites it

17 citing papers in PubMed.

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4 · The record

Corrections and comments

PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.

5 · Who and what money

Authors and funding

8 authors.

Matthew J TudballMRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.ORCID 0000-0002-7897-6180
Jack BowdenMRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.ORCID 0000-0003-2628-3304
Rachael A HughesMRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.ORCID 0000-0003-0766-1410
Amanda LyMRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.ORCID 0000-0002-4348-5146
Marcus R MunafòMRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.ORCID 0000-0002-4049-993X
Kate TillingMRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.ORCID 0000-0002-1010-8926
Qingyuan ZhaoDepartment of Pure Mathematics and Mathematical Statistics, University of Cambridge, Cambridge, UK.ORCID 0000-0001-9902-2768
George Davey SmithMRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.ORCID 0000-0002-1407-8314

Funding

Establishing Excellence in England (E3) Medical Research Council Integrative Epidemiology Unit at the University of Bristol MC_UU_00011/1Establishing Excellence in England (E3) Medical Research Council Integrative Epidemiology Unit at the University of Bristol MC_UU_00011/7Medical Research Council MC_UU_00011/1Medical Research Council MC_UU_00011/2Medical Research Council MC_UU_00011/3Medical Research Council MC_UU_00011/7Wellcome TrustWellcome Trust and the Royal Society 215408/Z/19/ZWellcome Trust and the Royal Society 220059/Z/19/ZWellcome Trust and the Royal Society 220067/Z/20/Z
6 · The paper itself

Abstract

A key assumption in Mendelian randomisation is that the relationship between the genetic instruments and the outcome is fully mediated by the exposure, known as the exclusion restriction assumption. However, in epidemiological studies, the exposure is often a coarsened approximation to some latent continuous trait. For example, latent liability to schizophrenia can be thought of as underlying the binary diagnosis measure. Genetically driven variation in the outcome can exist within categories of the exposure measurement, thus violating this assumption. We propose a framework to clarify this violation, deriving a simple expression for the resulting bias and showing that it may inflate or deflate effect estimates but will not reverse their sign. We then characterise a set of assumptions and a straight-forward method for estimating the effect of SD increases in the latent exposure. Our method relies on a sensitivity parameter which can be interpreted as the genetic variance of the latent exposure. We show that this method can be applied in both the one-sample and two-sample settings. We conclude by demonstrating our method in an applied example and reanalysing two papers which are likely to suffer from this type of bias, allowing meaningful interpretation of their effect sizes.

Indexed as

Mendelian Randomization AnalysisSchizophreniaBiasGenetic VariationHumansPhenotypebiomarkerslatent variable modellingMendelian randomisation analysissensitivity analysis

Identifiers

PMID33527565
PMCPMC8603937

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Registered trials

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Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.