Before revision: Given the following notation: effect of genetic variant on the exposure ; estimated effect of genetic variant g on the outcome ; estimated standard error of this estimated effect; MR estimate of the causal effect of the exposure on the outcome ; and considering the effect of a single genetic variant, the MR estimate can be obtained from the Wald ratio: When multiple genetic variants are used, the individual ratios for each genetic variants are combined using inverse variance weighting where each individual ratio is weighted by the uncertainty in their estimation.
After revision: Given the followin notation: effect of genetic variant on the exposure estimated effect of genetic variant g on the outcome estimated standard error of this estimated effect; MR estimate of the causal effect of the exposure on the outcome ; and considering the effect of a single genetic variant, the MR estimate can be obtained from the Wald ratio: When multiple genetic variants are used, the individual ratios for each genetic variants are combined using inverse variance weighting where each individual ratio is weighted by the uncertainty in their estimation.