Effect of a 1-month vs. a 12-month reference period on responses to the 14-item Oral Health Impact Profile.

The length of the reference period used in surveys of subjective oral health may have a marked influence on the responses obtained. We aimed to evaluate the effect of a 1-month (RP-1) vs. a 12-month (RP-12) reference period in the Oral Health Impact Profile (OHIP-14) questionnaire.