Chapter 19, Section 19.3

Study of Log C-Peptide Concentration in Children with Diabetes

Mixed Model Representation of Penalized Spline for Log C-Peptide Concentration

data tlc;

data diabetes;

infile 'diabetes.dat';

input age logc;

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* Create truncated line functions for piecewise linear curve with 10 knots at ages 5, 6, …,14 *;

***************************************************************************************************************;

bf1 = max(0,age-5);

bf2 = max(0,age-6);

bf3 = max(0,age-7);

bf4 = max(0,age-8);

bf5 = max(0,age-9);

bf6 = max(0,age-10);

bf7 = max(0,age-11);

bf8 = max(0,age-12);

bf9 = max(0,age-13);

bf10 = max(0,age-14);

title1 Mixed Model Representation of Penalized Spline for Log C-Peptide Concentration;

title2 Study of Log C-Peptide Concentration in Children with Diabetes;

proc mixed covtest;

model logc = age / solution outpred=yhat;

random bf1 bf2 bf3 bf4 bf5 bf6 bf7 bf8 bf9 bf10 / type=toep(1) solution;

run;

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* Use predicted values from the mixed model analysis to produce plot of fitted curve *;

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proc sort data=yhat;

by age;

proc gplot data=yhat;

plot pred*age;

symbol1 i=j;

run;