mids objects x and y into a
single mids object. The two mids objects should have the same
underlying multiple imputation model and should be fitted on exactly the same
dataset. If the number of imputations in x is m(x) and in
y is m(y) then the combination of both objects contains
m(x)+m(y) imputations.ibind(x, y)mids object.mids object.midsmids, rbind.mids, cbind.mids