William D. Dupont () (Department of Biostatistics, Vanderbilt University School of Medicine) Dale Plummer (Department of Biostatistics, Vanderbilt University School of Medicine)
Additional information is available for the following
registered author(s):
Restricted cubic splines (RCSs) are used with generalized linear models and other regression methods to model complex non-linear relationships. A RCS with k knots is linear before the first and after the last knot, is a cubic polynomial between adjacent knots, and is continuous and smooth. A RCS model with k knots can be fitted with only k-1 covariates. rc_spline calculates these covariates from an independent covariate and the knot values. Default numbers of knots and/or knot values suggested by Harrell (2001) may be used. We can then use the full power of Stata v9 to build models, construct graphs, and perform residual analyses using these covariates. RCSs are illustrated by modeling length of stay (LOS) and discharge mortality as a function of admission blood pressure (BP) from the SUPPORT study. LOS and log-odds of death are highly non-linear functions of BP. Multiple linear and logistic regression with RCSs are used to model these data. Plots of expected outcome with 95% confidence bands are easily overlaid on scatterplots using standard Stata graphics. These regression curves are little affected by the knot placements. This robust methodology is easily taught to non-statisticians and greatly expands the modeling capacity of standard regression methods.
Download Info
To download:
If you experience problems downloading a file, check if you have the
proper application to
view it first. Information about this may be contained
in the File-Format links below. In case of further problems read
the IDEAS help
page. Note that these files are not on the IDEAS
site. Please be patient as the files may be large.
Did you know? Citation analysis on IDEAS includes online papers that are freely accessible and whose text could be automatically analyzed, currently about 210000 papers.