st: mkspline and reg

["stata_user stata_user" <stata_dofile@hotmail.co.uk>]

Dear All,

I 've a variable age which takes values from 20 to 60,
I have an outcome y and a dummy variable represnting gender

I would like to fit a regresion model using linear splines, including an 
interraction effect

I want to test if there are two different slopes before 40 and after 40, and 
I am also interested on the intercept , I consider the following approach

1/ First create linear splines

mkspline age1 40 age2 = age

2/Second  in order to have intercept at age=40

generate age1a = age1 -40

3/
I fit a regression model

xi: regress y i.sex*age1a i.sex*age2

Could you please comment on this approach?

Thanks a lot

Sami

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