| APA | PPI. (2012, February 7). In Acronym Geek. Retrieved 22:54, February 7, 2012, from http://www.acronymgeek.com/PPI |
| MLA | "PPI." Acronym Geek. (2012). Acronym Geek. 7 Feb 2012 <http://www.acronymgeek.com/PPI>. |
| MHRA | 'PPI', Acronym Geek, 7 February 2012, <http://www.acronymgeek.com/PPI> [accessed 7 February 2012] |
| Chicago | "PPI", http://www.acronymgeek.com/PPI (accessed February 7, 2012). |
| CBE/CSE | PPI [Internet]. Acronym Geek; 2012 Feb 7 [cited 2012 Feb 7]. Available from: http://www.acronymgeek.com/PPI. |
| Bluebook | PPI, http://www.acronymgeek.com/PPI (last visited February 7, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, PPI, http://www.acronymgeek.com/PPI (optional description here) (as of Feb. 7, 2012, 22:54). |
| AMA | PPI. Acronym Geek. February 7, 2012, 22:54. Available at: http://www.acronymgeek.com/PPI. Accessed February 7, 2012, 22:54. |