Hi am have a clinical dataset of multiple observations per patient, with the number of visits varying widely. I want to find whether the baseline levels for each patient are abnormal (above a certain value), however, there are a few patients where the first value is missing for one of my variables on the first visit date, so I am struggling with this. At first I used first.id, but realized I wasn't putting everyone in the right boxes because of the missings Any advice how to approach this? id datechem CREAT AST ALKP TBILI N_VISITS 4 15MAR2018 0.8 19 58 0.5 6 4 16MAR2018 0.8 19 58 0.5 6 4 20MAR2018 0.7 18 . . 6 4 23MAR2018 0.6 23 . . 6 4 03APR2018 0.6 33 . . 6 4 06APR2018 0.7 29 . . 6 5 13JUL2018 . 36 135 . 7 5 18JUL2018 1.1 24 123 0.3 7 5 28JUL2018 0.9 23 92 0.3 7 2.01 07AUG1989 . . . . 7
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