@article {heckman_spline_1986,
	title = {Spline smoothing in a partly linear model},
	journal = {Journal of the Royal Statistical Society. Series B (Methodological)},
	year = {1986},
	pages = {244{\textendash}248},
	url = {http://www.jstor.org/stable/2345719},
	author = {Heckman, Nancy E.}
}
