split2 is a function which is used by the main function, mr_simss in order to perform the 2 split approach of the method, MR-SimSS.
split2(data, lambda.val = 0, pi = 0.5, mr_method = "mr_ivw", threshold = 5e-08)A data frame to be inputted by the user containing summary
statistics from the exposure and outcome GWASs. It must have at least five
columns with column names SNP, beta.exposure,
beta.outcome, se.exposure and se.outcome. Each row must
correspond to a unique SNP, identified by SNP.
A numerical value which is computed within the main function, mr_simss.
It is an estimate of lambda, a term used to describe the correlation between the SNP-outcome and
SNP-exposure effect sizes. The default setting is lambda.val=0.
A numerical value which determines the fraction of the first split. This is the fraction that will be used
for SNP selection. The default setting is pi=0.5.
A string which specifies the MR method that MR-SimSS works in
combination with. It is possible to use any method outputted in the list
TwoSampleMR::mr_method_list()$obj. However, it is currently advised
that the user chooses "mr_ivw" or "mr_raps". The default
setting is mr_method="mr_ivw".
A numerical value which specifies the threshold used to
select instrument SNPs for MR at each iteration. The default setting is
threshold=5e-8.
A data frame which contains
the output from one iteration. It is in a similar style as the output from
using the function mr from the TwoSampleMR R package. The MR method used, the number of instrument SNPs, the causal effect estimate, it associated standard error and p-value are all outputted.