Percentage points abbreviation

Solution 1:

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.

... are 5.2 pp more likely to ...

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.

"...percentage of uninsured Americans rose by 9 percentage points."

Solution 2:

How about percent or %?

Each of the following is common parlance:

... are 5.2 percent more likely to ...

... are 5.2% more likely to ...

There is no abbreviation that I am aware of of the sort you've mentioned, and personally I see no need for one.

Addendum: I answered the question that was originally asked. Based on the update to the question, it is now obvious that the OP is seeking an abbreviation for percentage points as per the example in the update. So, for example, if 30% changed to 24% for some reason, that change would correspond to a decrease of 6 percentage points. The question is this: Is there a best-practice (broadly-accepted?) abbreviation for percentage points? Personally, I am not aware of one, but any author could adopt an abbreviation, such as pp or ppt or ppts or %pts, provided they define it so the reader can understand it. Maybe some other user will have a more satisfying answer.

Addendum: See my comment below on the difference between using decrease and difference. In my first addendum, I should have used "difference of 6%" rather than "decrease of 6 percentage points". Had I used difference, there would have been no need to talk about percentage points at all. In fact, one often sees the term percent difference or % difference, either of which can be positive, negative, or zero.