Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.

# Re: st: Computing difference of counts within groups

 From Phil Schumm To statalist@hsphsun2.harvard.edu Subject Re: st: Computing difference of counts within groups Date Mon, 1 Nov 2010 11:09:20 -0500

```On Nov 1, 2010, at 10:46 AM, Grealy, Patrick J wrote:
```
I thought there was a simple way to do what I am attempting using the egen command but I have not gotten that to work right. Can someone make another suggestion? I am trying to check if the difference between two groups within another group exceeds a certain value. For example, using the auto dataset, within the five rep78 groups I would like to calculate the difference between Domestic and Foreign and check if it exceeds some limit, say 7.
```
```
This code below does what I want but I was hoping to find something simpler:
```
sysuse auto,clear
gen fdiff = .
foreach ix_rep78 of numlist 1/5 {
quietly count if foreign==0 & rep78==`ix_rep78'
local foreign0 `r(N)'
quietly count if foreign==1 & rep78==`ix_rep78'
local foreign1 `r(N)'
replace fdiff = abs(`foreign0' - `foreign1') if rep78==`ix_rep78'
}
tab rep78 foreign if fdiff > 7
```
```

One way to replicate exactly what you have done is the following:

egen fdiff = total((foreign*2)-1) if !mi(rep78), by(rep78)
replace fdiff = abs(fdiff)

-- Phil

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/
```