@misc{James2011,
author = {James, D. and Hornik, K.},
title= {chron: Chronological objects which can handle dates and times. R package},
year = {2011},
URL = {http://cran.r-project.org/web/packages/chron/index.html },
note = {(Accessed January 16, 2013)},
edition = {2.3-43},
}