@misc{Bates2012,
author = {Bates, D. and Maechler, M. and Bolker, B. },
title= {lme4: Linear mixed-effects models using S4 classes, 2011. R package version 0.999375-42},
year = {2012},
URL = {http://CRAN.Rproject.org/package=lme4},
}