SummaryThe effects of betel nut chewing, smoking and alcohol on the occurrence of leukoplakia and its malignant transformation to oral carcinoma were quantified in a leukoplakia cohort (n = 435) from one medical centre between 1988 and 1998 in Taiwan. Sixty oral carcinomas were ascertained in this cohort. A case-control study within the leukoplakia cohort was used to study, risk factors. Using the Weibull survival model, the incidence of malignant transformation of leukoplakia was shown to increase with follow-up years. After adjustment for other relevant risk factors, betel nut chewing (adjusted odds ratio (OR) = 4.59; 95% confidence interval (CI) 1.25-16.86) remained a significant risk factor for malignant transformation. Results from the case-control study showed that the adjusted odds ratios for betel nut chewing and smoking on the occurrence of leukoplakia were 17.43 (95% Cl 1.94-156.27) and 3.22 (95% Cl 1.06-9.78), respectively. Similar findings were observed when daily frequency and duration were taken into account. This implies that cessation of smoking may reduce by 36% leukoplakia cases, while elimination of betel nuts may prevent 62% of leukoplakia and 26% of malignant transformation to oral carcinoma in the underlying population.

No abstract

Recurrent event data are frequently encountered in studies with longitudinal designs. Let the recurrence time be the time between two successive recurrent events. Recurrence times can be treated as a type of correlated survival data in statistical analysis. In general, because of the ordinal nature of recurrence times, statistical methods that are appropriate for standard correlated survival data in marginal models may not be applicable to recurrence time data. Specifically, for estimating the marginal survival function, the Kaplan-Meier estimator derived from the pooled recurrence times serves as a consistent estimator for standard correlated survival data but not for recurrence time data. In this article we consider the problem of how to estimate the marginal survival function in nonparametric models. A class of nonparametric estimators is introduced. The appropriateness of the estimators is confirmed by statistical theory and simulations. Simulation and analysis from schizophrenia data are presented to illustrate the estimators' performance.

Tai chi can prevent a decline in functional balance and gait among older people. However, the reduction in injurious falls attained with tai chi did not reach statistical significance; the statistical inefficiency may have resulted partly from the large decline in injurious falls in control villagers. Finally, the unexpected effect of educational intervention on reducing injurious falls in different settings needs to be further examined.

Background and aims: The effect of metabolic risk factors on the natural course of gastro-oesophageal reflux disease (GORD), which remains elusive, was quantified. Methods: The population included 3669 subjects undergoing repeated upper endoscopy. Data were analysed using a three-state Markov model to estimate transition rates (according to the Los Angeles classification) regarding the natural course of the disease. Individual risk score together with the kinetic curve was derived by identifying significant factors responsible for the net force between progression and regression. Results: During three consecutive study periods, 12.2, 14.9 and 17.9% of subjects, respectively, progressed from non-erosive to erosive disease, whereas 42.5, 37.3 and 34.6%, respectively, regressed to the non-erosive stage. The annual transition rate from non-erosive to class A-B disease was 0.151 per person year (95% CI 0.136 to 0.165) and from class A-B to C-D was 0.079 per person year (95% CI 0.063 to 0.094). The regression rate from class A-B to non-erosive disease was 0.481 per person year (95% CI 0.425 to 0.536). Class C-D, however, appeared to be an absorbing state when not properly treated. Being male (relative risk (RR) 4.31; 95% CI 3.22 to 5.75), smoking (RR 1.20; 95% CI 1.03 to 1.39) or having metabolic syndrome (RR 1.75; 95% CI 1.29 to 2.38) independently increased the likelihood of progressing from a non-erosive to an erosive stage of disease and/or lowered the likelihood of disease regression. The short-term use of acid suppressants (RR 0.54; 95% CI 0.39 to 0.75) raised the likelihood of regression from erosive to non-erosive disease. Conclusions: Intraoesophageal damage is a dynamic and migratory process in which the metabolic syndrome is associated with accelerated progression to or attenuated regression from erosive states. These findings have important implications for the design of effective prevention and screening strategies.