Parameters for Models B, C and D based on diarrhea data from a Vitamin A trial in Brazil. Top Panel: Assumed gamma distribution for episode duration with parameters α = 0.8 and β = 2.7. The observed and simulated mean duration of episodes was 2.7 days. Middle panel: assumed gamma distribution for the number of episodes with parameters α = 1.2 and β = 6.8. The observed and simulated mean number of episodes per year was 7.0. Bottom panel: Correlation between incidence and episode duration. Diamonds indicate the mean episode duration of individuals according to individual incidence. The line indicates the regression line with a slope corresponding to an increase of 0.07 days in episode duration with every additional episode an individual experiences.