# Re: st: count (Stata 8)

 From Heather Gold <[email protected]> To [email protected], [email protected] Subject Re: st: count (Stata 8) Date Tue, 10 May 2005 11:44:09 -0400

Thanks for the replies thus far.
I'd prefer a scalar so I don't have to generate the extra variables with a value attached to each subject.

Based on all the comments you have generously offered, I'm closer to a solution:

forvalues i=1995/1998 {
count if dxflag==1 & year==`i'
scalar cases`i' = r(N)
count if year==`i'
scalar total`i' = r(N)
scalar prev`i' = cases`i'/total`i'
}
The problem is this doesn't give me different denominators (ie, total for each year)...thoughts?
Heather

```-------Original Message-------

```
Dear Listers -

I know this must be simple, but something eludes me.
I have a data set of subjects (cases and non-cases) by year and am trying to calculate a prevalence per year, ie, [cases/(cases+noncases)].
ie, data look like this:
id year dxflag
1 1995 1
1 1996 0
1 1997 0
2 1995 0
2 1996 1
...

I found that I can write
by year: count if dxflag==1
or
by year: count

and these return number of cases in the first line, and count of total population in the second line, just as I want.
But what I need are these values as scalars, so I can create a prevalence per year. In the Stata 8 help/manual it says that -count- saves the scalar of number of observations in r(N), but I can't seem to get this number to appear. Do I actually have to write a program to calculate this? And how does the "by year" part fit in...?

Heather

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:::::::::::::::::::::::::::::::::::::::::::::
Heather Taffet Gold, PhD
Assistant Professor
Department of Public Health
Weill Medical College of Cornell University
411 E. 69th Street
New York, New York 10021

E: [email protected]
P: (212) 746-1245
F: (212) 746-8544

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