Dear Statalist,
I have the following variable:
Code:
kVp Freq. Percent Cum. 80 20 0.03 0.03 90 30 0.05 0.08 100 11,999 18.03 18.1 110 1,202 1.81 19.91 120 45,807 68.83 88.74 130 5,049 7.59 96.32 135 1,037 1.56 97.88 140 1,411 2.12 100 Total 66,555 100
I looked at its effect in two ways:
as a continues variable:
Code:
xtset SurveyID_code xtgee CTDI kVp , corr(exchangeable) vce(robust)
Code:
xtset SurveyID_code xtgee CTDI i.kVp , corr(exchangeable) vce(robust)
How can I compare these two models and find out which one is the correct one?
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