To cite effects in publications use:

John Fox (2003). Effect Displays in R for Generalised Linear Models. Journal of Statistical Software, 8(15), 1-27. URL http://www.jstatsoft.org/v08/i15/.

For usage in multinomial and proportional-odds logit models also cite:

John Fox, Jangman Hong (2009). Effect Displays in R for Multinomial and Proportional-Odds Logit Models: Extensions to the effects Package. Journal of Statistical Software, 32(1), 1-24. URL http://www.jstatsoft.org/v32/i01/.

Corresponding BibTeX entries:

  @Article{,
    title = {Effect Displays in {R} for Generalised Linear Models},
    author = {John Fox},
    journal = {Journal of Statistical Software},
    year = {2003},
    volume = {8},
    number = {15},
    pages = {1--27},
    url = {http://www.jstatsoft.org/v08/i15/},
  }
  @Article{,
    title = {Effect Displays in {R} for Multinomial and
      Proportional-Odds Logit Models: Extensions to the {effects}
      Package},
    author = {John Fox and Jangman Hong},
    journal = {Journal of Statistical Software},
    year = {2009},
    volume = {32},
    number = {1},
    pages = {1--24},
    url = {http://www.jstatsoft.org/v32/i01/},
  }