Use of natural cubic splines for modeling pulmonary function in longitudinal epidemiological studies

M. Bottai
We present an application of natural cubic regression splines for the clinical practice in respiratory medicine. We derive reference equations for one pulmonary function index - the forced expiratory volume in one second (FEV1) - as a function of age, height, and body mass index (i.e. weight/height - squared), separately by gender. The non linear dependence of FEV1 on age is modeled by means of natural cubic splines with two breakpoints. They represent a simple...