Table 1. Glossary of MR Terms and potential uses in nutritional psychiatry 20 For more information about other terms and the.
| Term | Explanation |
|---|---|
| F-Statistic | The F-statistic measures the strength of genetic instruments. F<10 is suggestive of weak instrument bias. |
| Multivariable MR | Multivariable MR is a technique to account for pleiotropy due to multiple correlated exposures. |
| MR-PheWAS (MR Phenome Wide Association Study) | MR PheWAS is a method using a hypothesis-free approach to scan many outcomes for a given exposure using MR methodology. Such approaches could be used to test for and identify any potential adverse off-target effects of dietary supplementation, providing genetic instruments exist. |
| Pleiotropy | Horizontal Pleiotropy is where the SNP or SNPs related to the exposure are associated with the outcome through a pathway independent of the exposure (i.e. a violation of assumption c in figure 1b). Pleiotropy can be demonstrated by several methods, including Cochran’s Q statistic testing heterogeneity in causal estimates from each SNP, MREgger intercept, and leave-one-out analysis to identify influential outliers |
| Population Stratification | Spurious associations may arise in MR where the genetic variant and the outcome are associated with ancestral background in a mixed or stratified sample. Using genetic associations from within homogenous populations, or checking that the GWAS has controlled for population substructure in the analysis is important. |
| One-sample MR | Conventional one-sample MR uses a single sample in which exposure, outcome and genetic instrument are measured within the same population. One-sample MR may have power issues due to inadequate sample sizes of studies that are required to have genotype, exposure and outcome data. |
| Two-Sample MR | The estimates of the SNP-exposure and SNP-outcome associations used in MR analyses are identified in independent studies (usually genome-wide association studies) |
| Two-Step/Mediation MR | Two-step MR can be used to identify mediating mechanisms between an exposure and outcome using two steps- the first to assess the causal effect of the exposure on the potential mediator, and the second to assess the causal effect of the mediator on the outcome |