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st: RE: Using -byable- and the -by- commands correctly?


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Using -byable- and the -by- commands correctly?
Date   Mon, 31 Oct 2005 10:38:59 -0000

Please show us the whole program. 

Nick 
n.j.cox@durham.ac.uk 

David Winter
 
> 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?

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