Because behavior and mobility change dramatically with age, we frequently expect the force of infection to be age-dependent.  For example, in a study of contact rates in European countries, Mossong et al Mossong 2008 found that childrens’ contact rates increased dramatically at the age of school entry, which would be expected to correlation with an increased risk of exposure to various directly transmitted pathogens.  This age-dependent force of infection can be estimated from age-dependent serology or case records using the catalytic model.  This has been variously used for many childhood infections to identify high-risk age classes, which largely confirms the role of school entry as a major point of exposure to many infections EDMUNDS 2000.