why MR:
混杂因素confounding会影响outcom -> radomisation method but immoral -> MR
MR comes from Mendel’s Laws(segregation:randomly inheritance;independent assortment:no LD)
(当使用TWAS 混杂因素影响怎么去掉?)
3 MR core assumptions:
- SNP unrelates to confounders(in most case it is true. prove it by analyse one confounder with snp)
- population stratifation
- no horizontal pleiotropy (identify by sensitivity test)