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Re: st: AW: simple sum() question

From   Shehzad Ali <>
Subject   Re: st: AW: simple sum() question
Date   15 Apr 2009 16:54:45 +0100

Hi Martin and Josiane,

Thank you for your replies. You are right that I am interested in the total count of visits for each patient and not the running sum.

Sorry, I should have mentioned that patients who had three visits, for instance, have three observations, and those with two visits have two observations. Therefore, the total number of observations for 100 patients is less than 400 (I had made up hypothetical numbers in haste to simplify the case. Not always a good idea).

With Martin's solution, I will need to have four observations for each patient (sorry this was my fault as I didn't provide the correct information). With Josiane's suggestion, the dataset collapses which is not what I want.

Can you suggest a modified solution please? Again, sorry for the unclear email earlier.

Thank you, Shehzad

On Apr 15 2009, Martin Weiss wrote:

<> I am betting that you want a count of visits, not a running sum, but correct me if I am wrong...

set obs 400
egen float patient = seq(), from(1) to(400) block(4)
egen float visit = seq(), from(1) to(4) block(1)

//not strictly necessary
xtset patient visit

//less than 4 visits for some
replace visit =. if runiform()<0.05

bys patient: egen overallvisits=count(visit)

l in 1/20, sepby(patient) noo


-----Ursprüngliche Nachricht-----
[] Im Auftrag von Shehzad Ali
Gesendet: Mittwoch, 15. April 2009 16:48
Betreff: st: simple sum() question


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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Shehzad I Ali
Department of Social Policy & Social Work
University of York
YO10 5NG
+44 (0) 773-813-0094

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