The aim of the paper is to present the validation of a scale for assessing the impact of periodontal diseases on individuals' quality of life in Bulgaria. A pilot research was made among 30 diagnosed patients with periodontitis visiting the Department of Periodontology, Faculty of Dental Medicine, Medical University of Plovdiv, Bulgaria. The minimum sample size of 30 people was established based on a power analysis for sample size calculation. The mean age of participants was 48.95 ± 11.85 years, being 56.67 ± 9.05 years for males and 43.33 ± 9.05 years for females. Standard interviews were conducted using a specific instrument: self-designed questionnaire and a 5-degree ranked scale, containing initially 11 questions. The interviews were repeated after 3 months with the same patients for retest analysis. The data was statistically processed using SPSS v.13 software. Results received after the initial interviews: Cronbach's coefficient (α=0.882), Spearman-Brown coefficient (r sb=0.998), average inter-item correlation coefficient (R=0.426), difficulty of the questions from 0.173 to 0.757 and discrimination power from 0.405 to 0.809. Results after the second interviews: α=0.883, r sb=0.998, R=0.507, difficulty from 0.287 to 0.757 and discrimination power from 0.524 to 0.809. In two of the questions, a low level of inter-item correlation with the rest of the items was found and they were excluded. The final version of the questionnaire contained 9 questions. The validation proved that the developed scale is sufficiently reliable and will be used in the final research, the first one to use such an instrument for measuring oral health-related quality of life in Bulgaria.
periodontitis; quality of life; validation; scale
