I am writing an academic essay (APA standard) in which I compare a lot of proportions (and probability estimations).
Phrases like
… are 5.2 percentage points more likely to …
are common. So I want to use an abbreviation. But not sure if to use pps, PPs, pp, PPt, or just pp. Curiously, I find nothing from APA or anyone else when doing a quick web search looking for best practices. At this point any insights or standard I can follow is good enough.
Update
Percentage point is different from a percent (literally part of a hundred).
Example:
30 percent of customers complained about our service last year. This year
only 24 percent.
So we would say there has been 6 percentage points decrease in complaint but the decrease is also 0.06/0.30 = 0.2 = 20 percent.
Best Answer
I would suggest choosing any of these abbreviations, like pp, and clearly defining this for your readers at the beginning. I think using the abbreviation would actually make it less likely for someone to misinterpret what you are describing, since it is much more natural for people to assume we are discussing percent change (as evidenced by the initial interpretations of your question).
Wikipedia indicates that pp is used, but the reference provided seems to not directly support this. Other references indicate ppt may be used.
I would lean towards pp only because when I see ppt I think of "powerpoint" and this may be distracting for readers.
As a somewhat of an aside, this is definitely a less usual way of describing differences in proportions, so do be cautious about your phrasing. See this link for some examples of phrasing you might be able to use, which might even help clarify your point to your readers.