Change in Attachment Level

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Abstract
Attachement level or pocket depth measurements are used to detect change in periodontal attachement. However, measurement error limits their usefulness for this purpose. The aims of this study are twofold. The first aim was to test the assumption, used in previous reports of measurement error, that attachment level measurements are normally distributed. The second aim was to estimate error rates encountered when assessing periodontal attachement level change with attachement level or pocket depth measurements. Two simulation methods are compared in their ability to reproduce the distribution of differences in replicated measurements. A simulation method based on a normal distribution was not able to reproduce the atual distribution of differences between replicate measurements. In contrast simulations based on resampling recreated the distribution of differences in replicated attachement level measurements. Due to the inability of simulations based on the normal distribution to reproduce the distribution of differences in replicated measurements, simulations based on the resampling procedure were used to estimate error rates. Determining change in attachement level or pocket depth by either single or paired measurements resulted in low Type I error rates for both single and paired measurements. For single measurements of attachment level, the Type I error rate was 0.0074 for a 3-mm change. Paired measurements of attachment level had a Type I error rate of 0.0014 for a 3-mm change. However, false-positive rates were found to be much higher. For single measurements of attachment level, the false-positive rate was 0.32 for a 3-mm change. Taking two measurements at each time point reduced the proportion of false-positive by a factor of two: to 0.15 for 3-mm changes. Similar values were obtained for pocket depth measurements. This study demonstrates that a large proportin of perceived change in attachement level or pocket depth can be attributed to false positives.