st: RE: comparing two linear slopes

["Kieran McCaul" <Kieran.McCaul@uwa.edu.au>]

...


just out of curiosity, how did you establish that the relationship was
linear for the intervening years?



-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Ashwin
Ananthakrishnan
Sent: Saturday, 30 October 2010 4:40 AM
To: statalist@hsphsun2.harvard.edu
Subject: st: comparing two linear slopes

Hi, 

I'm examining the rate of change of two proportions over time. I'd be
grateful if someone could help me figure this out: 

I'm looking at the proportional increase in two specific disease (as a
proportion of all hospitalizations) over time and need to see if the
rate of increase for one disease is statistically greater than the rate
of increase for disease 2. 

I have the sum totals for the numerators (i.e disease 1 or disease 2)
and denominators (total hospitalization 1 and total hospitalizations 2)
for the start and the end year (the relationship is linear for the
intervening years - that's been looked at). 

Is there a way to compare these two trends statistically to say that the
4-fold increase for disease 1 is significant greater than the 2-fold
increase for disease 2? 

Should i calculate the annual percent change for each disease and then
use the two-sample t test? How i get the Std dev for the annual percent
change? 

Thanks, 

Ashwin


      
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