Biostatistics Advance Access originally published online on October 24, 2006
Biostatistics 2007 8(3):654-673; doi:10.1093/biostatistics/kxl036
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Generalized monotonic regression based on B-splines with an application to air pollution data
Department of Statistics, Ludwig-Maximilians-Universität München, Akademiestraße 1, 80799 München, Germany florian.leitenstorfer{at}stat.uni-muenchen.de
* To whom correspondence should be addressed.
In many studies, it is known that one or more of the covariates have a monotonic effect on the response variable. In these circumstances, standard fitting methods for generalized additive models (GAMs) generate implausible results. A fitting procedure is proposed that incorporates monotonicity assumptions on one or more smooth components within a GAM framework. The algorithm uses the monotonicity restriction for B-spline coefficients and provides componentwise selection of smooth components. Stopping criteria and approximate pointwise confidence bands are derived. The method is applied to the data from a study conducted in the metropolitan area of São Paulo, Brazil, where the influence of several air pollutants like SO2 on respiratory mortality is investigated.
Keywords: Air pollution data; Generalized additive models; Likelihood-based boosting; Monotonic regression
Received June 2, 2005; revised March 21, 2006; revised July 27, 2006; accepted for publication October 20, 2006.