> Thx to M. Perticara and N. Cox. I reviewed the -ineq- as suggested, and
> as part time stata user, I might not have the background to adequately
> understand what was implemented so I thought I would give it another try.
> I am trying to calculate a focus index (I'm not sure the Simpson was the
> same). In any event, it is a simple measure. If I assume a car
> manufacture makes 3 cars in 3 separate classes, they would have a focus
> measure of 1/3. (1^2 + 1^2 + 1^2)/3^2 = 3/9. On the other hand, if one
> manufacturer makes 3 cars all in one class, the focus measure would be
> (1+1+1)^2/3^2 = 9/9 or 1.00.
>
> If I drop all observations except for one manufacturer, the following code
> works fine:
>
> /* This sequence calculates the focus variables */
> tab class, matcell(classmat)
> mat nummat=catmat'*catmat
> gen numerator=nummat[1,1]
> gen denominator=(_N)^2
> gen focus=numerator/denominator
> list focus
>
> My problem is I have many 'manufacturers'. When I try to implement this
> code with the "by:" syntax, I continue to have difficulties. I would like
> to keep the data in this format/shape because I have generated several
> other variables by 'manufacturer'.
>
> Any thoughts or suggestions are greatly appreciated. Thx again - SF
>
> Steve Fraser
> Univ of South Florida
>
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