MR Dictionary

Relevance assumption

Synonyms: IV1 assumption, first MR assumption

This is the first of the core MR assumptions which states that the instrumental variable (IV) must be associated with the exposure of interest. 

In MR the aim is to select genetic variants that have been shown to be robustly associated with the exposure of interest. In most MR studies, this means genetic variants that are associated with an exposure at genome-wide significance and replicated in several independent study samples from the population of interest. If the statistical strength of the association between the genetic IV and exposure is weak, this can result in weak instrument bias


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