Abstract
A general framework for smooth regression of a functional response on one or multiple functional predictors is proposed. Using the mixed model representation of penalized regression expands the scope of function-on-function regression to many realistic scenarios. In particular, the approach can accommodate a densely or sparsely sampled functional response as well as multiple functional predictors that are observed on the same or different domains than the functional response, on a dense or sparse grid, and with or without noise. It also allows for seamless integration of continuous or categorical covariates and provides approximate confidence intervals as a by-product of the mixed model inference. The proposed methods are accompanied by easy to use and robust software implemented in the pffr function of the R package refund. Methodological developments are general, but were inspired by and applied to a diffusion tensor imaging brain tractography dataset.
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Acknowledgments
Staicu’s research was supported by U.S. National Science Foundation Grant Number DMS 1007466 and by the NCSU Faculty Research and Professional Development Grant. Fabian Scheipl and Sonja Greven were funded by Emmy Noether Grant GR 3793/1-1 from the German Research Foundation. We thank Daniel Reich and Peter Calabresi for the DTI tractography data. We would like to thank Ciprian Crainiceanu for helpful discussions and comments on earlier versions of the paper.
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The refund package is available from CRAN at the following website: http://CRAN.R-project.org/package=refund.
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Ivanescu, A.E., Staicu, AM., Scheipl, F. et al. Penalized function-on-function regression. Comput Stat 30, 539–568 (2015). https://doi.org/10.1007/s00180-014-0548-4
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DOI: https://doi.org/10.1007/s00180-014-0548-4