• age;
  • cohort analysis;
  • cohort effects;
  • oral health change;
  • period

Abstract –Objectives: The purpose of this analysis was to study temporal variation in oral health in an adult population. The cohort analysis comprised 1) estimation of longitudinal, cross-sectional, and time-lag differences in caries and treatment experience of the adult population in Trøndelag from 1973 to 1983 and to 1994; 2) assessment of which of the effects of age, period and cohort was the most plausible explanation for the observed differences and 3) discussion of causal and other factors underlying the effects of age, period and cohort. Methods: Cohort analysis was used to study changes in oral health over time. Study participants were selected by random sampling in 1973, 1983, and 1994 (n=1959, n=3195, n=2341 respectively). The methods of data collection comprised standardised clinical measurements and a self-administered questionnaire. Cohort tables were established to analyse changes in DFT from 1973 to 1983 and DFT and DFS from 1983 to 1994. Results: Four patterns of changes in oral health were identified from adolescence to older adulthood. They point in different directions which indicate that complex processes are present. There were two and three significant changes in the subsets of analysis. Assumptions and conditions that allow identification of separate cohort, period, and age effects appeared not to be present. The pattern of changes was consistent with main effects of both age, period, and cohort. The effects were discussed from the perspective of the chosen frame of explanatory factors. Conclusions: The changes in oral health between populations in 1973, 1983 and 1994 were the combined consequences of simultaneously occurring factors that account for both age, period and cohort effects.