Comparing measures of reliability for indices of gingivitis and plaque.

The purpose of this methodological study was to compare methods used to assess reliability for gingival inflammation and plaque. Duplicate examinations were conducted by one examiner on 17 subjects (506 scoring sites), using the gingival index (GI), bleeding points index (BPI), and plaque index (PI). The percentage of agreement, the weighted and unweighted kappa coefficients, and Pearson correlation coefficients were calculated as statistics of reliability for mesial buccal site scores and whole mouth mean scores when appropriate. For mesial buccal sites the respective values of the GI, BPI, and PI for weighted kappas were: 0.47, 0.49, and 0.75; for the correlation coefficients: 0.47, 0.49, and 0.76; for unweighted kappas, 0.39, 0.49, and 0.39; and for percentage of agreement 66.2%, 76.1%, and 51.2%. For whole mouth means the correlation coefficients for the GI, BPI, and PI were 0.87, 0.59, and 0.87, respectively. In conclusion, the most useful statistics in assessing the intraexaminer reliability of a solo examiner in descending order were the weighted kappa coefficient, Pearson correlation coefficient, the unweighted kappa coefficient, and percentage of agreement.