Dear Statalisters,
Firstly, thanks to Svend Juul for the helpful comments on survival
analysis.
The following 4 records are part of a 27 record dataset sorted by
ageband (5,10,15,20..85) within sex (MALE,FEMALE).
Sex Ageband Observed Expected PoissStat
MALE 5 5 .2585
MALE 10 11 .6054
MALE 15 6 .6516
MALE 20 5 .6435
I have written a program to calculate a two-tailed poisson statistic,
that has three arguements:
`1' = Observed number
`2' = Expected number
`3' = variable to hold the poisson statistic
I have made the program -byable- :
Program poissontt, sortpreserve byable(recall, no header)
..
..
local poissval = 0 /* macro to store the result */
..
local observed = `1'
local expected =`2'
local replacevar = "replace `3' = "
..
<define poissval>
..
`replacevar' `poissval'
end
In a -.do- file, I run the commands
gen PoissStat = .
by sex ageband: poissontt Observed Expected PoissStat
Stata diligently loops through the data and using -set trace- I have
tracked the iterations. It does not appear to pick up the values of
Observed and Expected for each record, rather those of the first record
only. The calculation is correct for record 1 (Obs=5, Expect=.258,
poisson(two-tailed=.0000153) and the PoissStat variable is updated in
each record, but with the value for record 1 only.
Is there something I am missing either in the program or in using the
-by- command?
With Best Wishes,
Dave
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