Aim/Objectives:

The major aim of the present study would be to examine how early life (i.e. parenting practices and genetic parental proxies as well as psychopathology problems during childhood) and early adolescent variables (i.e. adolescent risky sexual and substance use behaviours as well as adolescent psychopathology problems) jointly influence later ("distal") disease outcome such as Chlamydia infection during middle and late adolescence (i.e. 17-22 years old) or/and teenage pregancies. We would test hypotheses about the mechanisms by which contextual factors or developmental processes affect developmental change and ultimately chlamydia infection at the age-range of 17-22 years old and teenage pregnancies. We will be considering methods that not only consider the longitudinal nature of the data, but also maintain the distinction between intra-and inter-individual change. Careful consideration would be given to aspects such as measurement error, the theory of change for the variables in the model, the critical role of time in interpreting results, and the variety of possible indirect effects that will be a part of each considered model. Different approaches of causal mediation modelling would be considered while a range of sensitivity analyses would be performed in order to estimate and evaluate the assumptions for causal interpretation. Although ALSPAC contains a wealth of data at different ages that enables assessment of these pathways, it also introduces a number of additional methodological challenges such as missing data problems or low power for some socio-economic or/and geographically variable exposures. For instance, children from lower socioeconomic groups were more likely to drop out of ALSPAC over time and for those who remained in the study a very low prevalence of C. trachomatis are currently found.