Which figure of speech is used in this text?
Although the researchers did produce statistically significant results, their sample size was small. They seemed to be slightly economical with the truth when they claimed that their study was generalizable to the greater population.

 - euphemism
 - chiasmus
The text uses a euphemism, a polite or indirect expression that is used to de-emphasize an unpleasant topic.
Economical with the truth is an indirect way of indicating that someone is lying or misrepresenting the truth.