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st: simple sum() question

From   Shehzad Ali <>
Subject   st: simple sum() question
Date   15 Apr 2009 15:47:56 +0100


I have a simple question about summing across observations. I have 100 patients (variable: patient_id) in the dataset, each had clinic visits (variable: clinic) and hospital visits (variable: hospital) recorded at weeks 4, 8, 12 and 16. The dataset is long and hence I have 400 observations (one observation per patient per time point).

I want to sum the clinic visits for each patient (across all 4 visits) bearing in mind that some patients had less than 4 visits. So effectively I want to generate a new variable that will produce the sum of clinic visits for each patient.

Any help would be appreciated.

Thank you,
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