Exposure-Response Modeling

32 Exposure-Response Modeling: Methods and Practical Implementation

other approaches that use more information in the data in later par ts of the

book.

Using spline functions in SAS is also easy for some proce dures such as proc

GLIMMIX. The EFFECT statement

EFFECT bs = spline(exposure / knotmethod=percentiles(3));

creates B-spline function effects with two knots at the lower and upper bo unds

and internal knots at the median of the e xposure data. Then in the model

statement the effects bs are included as covariates. This statement can be

used in a number of other SAS procedures.

As a general approach, creating B-spline functions as covariates outside of

a procedure or function for model fitting can be used in almost all s oftware

including R/Splus functions ...