| APA | PPD. (2012, February 14). In Acronym Geek. Retrieved 06:59, February 14, 2012, from http://www.acronymgeek.com/PPD |
| MLA | "PPD." Acronym Geek. (2012). Acronym Geek. 14 Feb 2012 <http://www.acronymgeek.com/PPD>. |
| MHRA | 'PPD', Acronym Geek, 14 February 2012, <http://www.acronymgeek.com/PPD> [accessed 14 February 2012] |
| Chicago | "PPD", http://www.acronymgeek.com/PPD (accessed February 14, 2012). |
| CBE/CSE | PPD [Internet]. Acronym Geek; 2012 Feb 14 [cited 2012 Feb 14]. Available from: http://www.acronymgeek.com/PPD. |
| Bluebook | PPD, http://www.acronymgeek.com/PPD (last visited February 14, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, PPD, http://www.acronymgeek.com/PPD (optional description here) (as of Feb. 14, 2012, 06:59). |
| AMA | PPD. Acronym Geek. February 14, 2012, 06:59. Available at: http://www.acronymgeek.com/PPD. Accessed February 14, 2012, 06:59. |