Re: st: RE: creating variable

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

Thanks for the help! The exam is indeed mine and you can share in my A!!
Peggy

Nick Cox wrote:
> The nub of the problem is this. Consider these data: 
> month   sales (sales of Stata 10) 
> 1         1 million
> 2         1 billion 
> 3         1 trillion 
> Then 
> gen sales1 = sales if month == 1 
> gen sales2 = sales if month == 2 
> gen sales3 = sales if month == 3 
> creates these variables 
> month  sales1          sales2           sales3 
> 1      1 million         .                . 
> 2      .               1 billion          . 
> 3      .                 .             1 trillion
>
> Now when you average, your averages will be all
> missing, as they are all based on the sum of 
> one value and two missings, which in Stata is missing. 
> You are averaging across observations. You need
> to average in columns. 
> Check out, for example, -tssmooth-. 
> (If the take home exam is yours, do I get to share
> your grade?) 
> Nick 
> n.j.cox@durham.ac.uk 
> P chrisman
>  
>   
> > 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.
> >
> >     
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