(A) A model describing the risk of developing active tuberculosis in Norway as a function of time (in years) after infection. The model is based on data from Ferebee  up to ten years after infection. The curve was extended beyond 10 years based on the expected decline in the risk of development of tuberculosis as determined by the cohort analysis of this study. (B) This model shows the rate of clearance of latent tuberculosis from a population where all persons have been infected, and assuming that transmission of tuberculosis was completely stopped at time 0. The cohort analysis showed an average rate of 57% decline of tuberculosis over a 10 year period, and this was used as the basis for this model. Clearance by natural death was not considered.