*
* Example 6.3 from page 195
*
open data attend.raw
data(format=free,org=columns) 1 680 attend termgpa prigpa act final atndrte hwrte frosh soph skipped stndfnl
*
set prigpasq = prigpa**2
set actsq    = act**2
set gpabyatndrte = prigpa*atndrte
*
linreg stndfnl
# constant atndrte prigpa act prigpasq actsq gpabyatndrte
*
* Test the two attendance rate variables
*
exclude
# atndrte gpabyatndrte
*
stats prigpa
compute gpamean=%mean
*
* This will compute the value and the standard error for the function of the coefficients
*
summarize(title="Effect of Attendance Rate at Mean GPA") %beta(2)+%beta(7)*gpamean
*
* Doing this by reparameterizing the regression
*
set centered = (prigpa-gpamean)*atndrte
linreg stndfnl
# constant atndrte prigpa act prigpasq actsq centered
*
* Reparameterize the GPA squared term as well
*
set centgpasq = (prigpa-gpamean)**2
linreg stndfnl
# constant atndrte prigpa act centgpasq actsq centered