Determining the minimal important difference of the Oral Health Impact Profile for Chronic Periodontitis (OHIP-CP).

AIM: Building on previous psychometric work, we aimed to further assess the minimally important difference (MID) of the Oral Health Impact Profile for Chronic Periodontitis (OHIP-CP).

METHODS: In total, 240 consecutive patients with chronic periodontitis were recruited in the study. The OHIP-CP was completed at baseline and after six weeks. Methodology testing included the confirmatory factor analysis (CFA), and minimal important difference (MID). Confirmatory factor analysis (CFA) was performed to assess the fit of the previously proposed three-factor model. The MID of this questionnaire was determined by applying anchor-based and distribution-based approaches.

RESULTS: The CFA supported a three-factor model for the OHIP-CP with acceptable fit to the data. The fit indices were χ2 /df=2.231, GFI=0.935, TLI= 0.969, CFI=0.976, RMSEA=0.076. The OHIP-CP scores showed significant improvements after treatment (P<0.001). The anchor-based MIDs of OHIP-CP for 'oral function restriction', 'oral pain', 'psychological and social impact', and total score were 2, 1, 4, and 7 points, respectively. The effect sizes (ES) and standardized response mean (SRM) for the OHIP-CP were moderate to large.

CONCLUSIONS: The MID of the OHIP-CP is recommended for interpreting clinically meaningful change in oral health-related quality of life (OHRQoL) over time.