USE OF THE WEIBULL HAZARD MODEL TO ESTIMATE AGE-SPECIFIC PROBABILITY OF PERMANENT TOOTH LOSS

In analysis of the probability of tooth loss with age, the exact time of tooth loss is often unknown, although it is clear whether a tooth r emains or has been lost. That is, left censoring is inevitable during data sampling. This may provide a biased estimate if such data are dea lt with by the product-limit method, which is a common method of survi val analysis. To reduce such a bias in estimating the age-specific pro bability of tooth loss, we developed a survival analysis method taking left censoring into consideration. Four hundred and forty-six panoram ic radiographs obtained in a daily clinical practice were used. The fr equency of tooth loss with age was assumed to follow the Weibull hazar d model, and a likelihood function taking left censoring into consider ation was defined to estimate the probability of tooth loss. The estim ate obtained from our method was compared with that from the product-l imit method to examine whether the effect of left censoring was reduce d. We found that the probability of tooth loss estimated by the produc t-limit method was biased by left-censored data, and that the bias was reduced when our method was used. A Monte Carlo simulation study, in which the true tooth loss time was given, also showed that our method provided an estimate closer to the true value. Our method is considere d to be more accurate in estimating the probability of tooth loss, sin ce it reduces the bias caused by left-censored data.