Fixes pram

[MuellerRoman]

Pull request regarding issue: #358

Summary

Fix PRAM behavior when strata variables are used. Previously PRAM was not applied within subgroups; now PRAM is applied within strata.

Changes

• Adjusted pram.R (row 510 - 516)
• Rs <- calcTransitionMatrix(xvec=data[[v]][ii], pd=pd[[i]], alpha=alpha[[i]]) is now within the for loop.
• changed data[[v]] in calcTransitionMatrix to data[[v]][ii]

Testing

• No devtools::check() added
• Manual test: I ran the test script (see pram() is not correctly applied within subgroups #358) again and checked whether pram is now only applied within the subgroups.
• Further testing may be necessary to prevent errors from occurring in other locations.