@article {greven,
	title = {Longitudinal functional principal components analysis},
	journal = {Electronic Journal of Statistics, PMCID: PMC3131008},
	volume = {4},
	year = {2010},
	pages = {1022-1054},
	author = {Greven, S. and Crainiceanu, C and Caffo, B and Reich, D.}
}
