Within-mouth correlations and reliabilities for probing depth and attachment level.

Replicate measurements of probing depth and attachment level were made by three examiners on the six Ramfjord teeth of 34 patients. Within-mouth correlations were high for single measurements, and yet higher for means across replicate measurements. Inter- and intra-examiner variability were both found to be low relative to between-patient variability. Conclusions are that the low within-mouth correlations reported by others may be the result of poor reliability, and that it is inappropriate to take the individual site as the unit of statistical analysis in clinical studies of periodontitis.