[R] Help with slope comparisons

[Ravi Kulkarni]

Hello Forum,
  I have data for two groups of subjects for a ratio variable (cortisol
level) assessed three times during the day (at 0600, 0900 and 2100 hours).
So I have three means for each group. I have been asked to do a "slope
analysis" to compare the two groups.
  According to my understanding, this means that I regress the three means
on the time for each group and compare the slopes using a t-test (there is a
post on this: Etienne Toffin etoffin at ulb.ac.be
Tue Jan 27 20:08:36 CET 2009).
  My question: (if what I said is correct) it seems strange to me that we
calculate a regression line with just three data points - is this really
what is meant by a "slope analysis"? 

  Any help most appreciated...

  Ravi
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