APA   Click to copy
Nielson, D., & Shugart, M. (1999). Constitutional Change in Colombia.

Chicago/Turabian   Click to copy
Nielson, D., and M. Shugart. “Constitutional Change in Colombia” (1999).

MLA   Click to copy
Nielson, D., and M. Shugart. Constitutional Change in Colombia. 1999.

@article{d1999a,
  title = {Constitutional Change in Colombia},
  year = {1999},
  author = {Nielson, D. and Shugart, M.}
}