st: creating variable

[P chrisman <peggyc@u.washington.edu>]

Dear List,

I have a longitudinal data set with 12 records for each subject for a 
take home final exam. I need to create an average iron dose measurement 
for the first months of the 12 months study period. I have tried the 
following in long format:

gen ironm1=iron if month==1
(11132 missing values generated)

. gen ironm2=iron if month==2
(11134 missing values generated)

. gen ironm3=iron if month==3
(11135 missing values generated)

. gen ironBL=( ironm1+ ironm2+ ironm3)/3
(12144 missing values generated)

The problem is that my ironBL variable is "missing" data for all 
subjects rather than the average of the 3 iron measurements.

I also tried the following in wide format:

gen ironBL=(iron1+iron2+iron3)/3
(4 missing values generated)

I honestly do not understand what went wrong here. I thought perhaps 
egen ironBL=mean(iron) if month<=3, but that does not work either.

Thanks,
peggy

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