To cite the WWGbook package in publications use:

West B, Welch K, Galecki A (2006). Linear Mixed Models: A Practical Guide Using Statistical Software, First edition. Chapman Hall / CRC Press. ISBN 1584884800, http://www-personal.umich.edu/~bwest/almmussp.html.

Corresponding BibTeX entry:

  @Book{,
    title = {Linear Mixed Models: A Practical Guide Using Statistical
      Software},
    author = {B. West and K. Welch and A. Galecki},
    publisher = {Chapman Hall / CRC Press},
    edition = {First},
    year = {2006},
    note = {ISBN 1584884800},
    url = {http://www-personal.umich.edu/~bwest/almmussp.html},
  }