@article{Nagin1999,
author = {Nagin, D.S.},
title= {Analyzing developmental trajectories: A semiparametric, group-based approach},
year = {1999},
doi = {10.1037/1082-989X.4.2.139},
journal = {Psychological Methods},
volume = {4},
number = {2},
pages = {139--57},
}