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Two robust tools for inference about causal effects with invalid instruments
Author(s) -
Kang Hyunseung,
Lee Youjin,
Cai T. Tony,
Small Dylan S.
Publication year - 2022
Publication title -
biometrics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.298
H-Index - 130
eISSN - 1541-0420
pISSN - 0006-341X
DOI - 10.1111/biom.13415
Subject(s) - instrumental variable , causal inference , mendelian randomization , inference , econometrics , outcome (game theory) , confidence interval , confounding , statistics , variable (mathematics) , causal model , computer science , mathematics , artificial intelligence , mathematical analysis , biochemistry , chemistry , mathematical economics , genetic variants , genotype , gene
Instrumental variables have been widely used to estimate the causal effect of a treatment on an outcome. Existing confidence intervals for causal effects based on instrumental variables assume that all of the putative instrumental variables are valid; a valid instrumental variable is a variable that affects the outcome only by affecting the treatment and is not related to unmeasured confounders. However, in practice, some of the putative instrumental variables are likely to be invalid. This paper presents two tools to conduct valid inference and tests in the presence of invalid instruments. First, we propose a simple and general approach to construct confidence intervals based on taking unions of well‐known confidence intervals. Second, we propose a novel test for the null causal effect based on a collider bias. Our two proposals outperform traditional instrumental variable confidence intervals when invalid instruments are present and can also be used as a sensitivity analysis when there is concern that instrumental variables assumptions are violated. The new approach is applied to a Mendelian randomization study on the causal effect of low‐density lipoprotein on globulin levels.