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st: Area under the curve trouble with aucdist

Subject   st: Area under the curve trouble with aucdist
Date   Tue, 24 Sep 2002 13:05:12 -0500

I need to calculate the area under the curve (viral load over time) for
about 1000 study participants using the trapezoidal rule.  I have used
aucdist but I am not getting a result and am not sure if I'm getting an
error message.

id = patient id
time =  time of viral load test
conc = viral load value

aucdist   id   time   conc,   t  generate(auc)

(t specifies that the integral be computed using the simple trapezoidal
rule, and generate(auc) specifies to create a new variable with the AUC (C
max, T max, log conc 0 -inf.))

but all I'm getting is  (2000) in return which is supposed to mean that I
have no observations on which to perform the statistical operation.

I have 9500 observations with multiple observations per patient, there are
no missing data.  Any suggestions as to what I may be doing wrong?
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