I am trying to repeat the word "Difference-in-Differences" in my paper many times. I am using "DiD" instead (but I am not sure whether it is true or not). I am looking for any other way to write "Difference-in-Differences" in short version in an academic paper.
I would suggest picking one and using it consistently throughout your paper. Common abbreviations include DD, DiD, and Diff-in-Diff.
As a technique, difference-in-differences is actually a double difference estimator, though this description is rarely used in academic papers. It’s only when authors also estimate difference-in-difference-in-differences, then the term triple difference estimator seems to be preferred.
I derive my opinion from a survey of the literature in economics, political science, and criminology, but other abbreviations may be preferred in other disciplines. If I had to choose, I would go with either DD or DiD, though I tilt a bit more toward the latter.