MR Dictionary

A statistic used to estimate the variance explained in dependent variable by the instrumental variable (IV).

In MR analyses, this is typically used to estimate the variance explained in the exposure of interest by the genetic IV. Coupled with various other statistics describing the sample and parameters being used to estimate the causal effect of the exposure on the outcome (e.g., sample size, type-1 error rate, the hypothesised regression coefficient of the causal relationship of the exposure and outcome, and the variance of the continuous exposure and continuous outcome of interest or the proportion of cases vs. controls for binary outcomes), the R-squared can be used to estimate statistical power in MR analyses. The R-squared can be calculated with individual-level data using linear or logistic regression of the exposure and the genetic IV. The R-squared can also be estimated using summary-level data for two-sample MR, which typically uses one or more single nucleotide polymorphisms (SNPs) associated with the exposure as the genetic IV, if the required statistics are available for each SNP (e.g., the beta coefficient, standard error and sample size of the association between the SNP and exposure and the minor allele frequency of the SNP).


Other terms in 'Sources of bias and limitations in MR':