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st: survival analysis - interaction


From   Lucy Shum <[email protected]>
To   [email protected]
Subject   st: survival analysis - interaction
Date   Mon, 1 Jan 2007 19:20:48 +1100

Hi all~

How does one interpret the following command:

xi: stcox i.mastitis*i.age, robust

this is enquiring the proportional hazard of interaction between age
and mastitis, correct?
So would it be "whether the effect of mastitis increases or decreases
with age.."?

Supposingly, there should be no difference in the order of the
covariates, ie.,

xi: stcox i.mastitis*i.age, robust  versus,
xi: stcox i.age*i.mastitis, robust

However, the output is distinctly different. Anyone got comments?

Hope you all had a good and festive New Year's Eve!

Cheers

Lucy


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