Re: st: comparing differences of rate differences

[Philip Ryan <philip.ryan@adelaide.edu.au>]

Depending on whether your "rates" are true incidence densities or 
cumulative rates (treated as proportions as your current analyses imply) 
you could use either the -ir- or -cs- commands of the epitab suite  (see 
-help epitab-). The  binary exposure variable is the year   and 
the   -by()-  option would have race as a 0/1 variable as its 
argument.  The test for heterogeneity is a rather non-powerful test of 
whether the effect of year on admission differs between the races.

Alternatively, model it (using -poisson- or -binreg- depending on your 
conception of the rate and the metric you wish to use) with a 
year*race  interaction term.

eg for risk differences:

binreg  admitted  year  race  year_X_race, rd

The coefficient on the interaction term is of interest.

Phil




At 04:15 PM 9/03/2004 -0800, you wrote:

> Dear all,
>
> This is not really a Stata question but I have been
> unsuccessful finding a satisfactory answer. Any
> assistance will be greatly appreciated.
>
> I have computed hospital admission rates for two
> different years (1996, 2002). To compare these rates I
> can simply use Stata�s �prtest- (or �tabulate- ) to
> test whether these rates differ.
>
> Now, if I compute these rates separately for Whites
> and Blacks, how can I test if the change in rates from
> 1996 to 2002 is different for whites than for blacks?
>
> Thank you,
> Ricardo.
>
>
> =====
> Ricardo Ovaldia, MS
> Statistician
> Oklahoma City, OK
>
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Philip Ryan
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