st: Summarising multiple visit data for each individual participant

[Matthew Hurley <Matthew.Hurley@nottingham.ac.uk>]

Dear all,
I would be grateful for your help as I cannot find a solution in the archives or online.

I have patient registry data for which visit data is grouped by patient ID.  At each visit individuals are administered an antibiotic.  I wish to determine if specific antibiotic usage in this dataset is associated with infection in a survival analysis.

I have completed the survival analysis assuming that the antibiotic taken on the first visit represents all antibiotic taken throughout the period, however this assumption is incorrect as antibiotic usage changes on some occasions.

Is there a way I can 'summarise' each individual patients antibiotic use please?  The most pragmatic solution I can think of is to perform a sensitivity analysis for those patients whose antibiotic usage does not change (e.g. for the first 3 visits) to see if this changes my results.

I have tried by generating an indicator variable 'visitno'. 'chrpo' is my categorical variable that reports the antibiotic taken at each visit - generating a 'sumabx' variable that reports the consistently administered antibiotic for each patient.

by ID ( visitno), sort: gen sumabx = chrpo if chrpo[1]== chrpo[2]== chrpo[3] ....however this doesn't work.
I have a separate indicator variable that selects the first visit per patient.

Apologies if this is a really rudimentary question that highlights my ignorance, but I genuinely cannot find the solution anywhere.

Best wishes,
Matt
Clinical Research Fellow
University of Nottingham
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