LifeSim childhood: extrapolating intervention effects and public cost savings from birth to adolescence in the UK

Economic evaluation of early childhood interventions is challenging because it is hard to extrapolate the full range of long-term benefits and public cost savings from short-term effectiveness evidence. One way to address this issue is through the use of microsimulation. This paper introduces a closed birth cohort childhood microsimulation model, LifeSim Childhood, that is capable of extrapolating the long-term effects of various childhood circumstances on a broad range of health, educational, and social outcomes and public cost savings up to age 17 in the UK. We use regression-based long-jump microsimulation that simulates outcomes at each age directly from total-effect parameters estimated using bespoke longitudinal birth-cohort regressions, without tracing indirect mediating pathways. The aims of this paper are to describe the general modelling approach and methods underpinning LifeSim Childhood, to present a simple illustration of how the model can be used to simulate the effects of reducing early childhood poverty, and to compare our illustrative results with estimates from quasi-experimental studies. We use data from the Millennium Cohort Study which follows children born in the UK around the year 2000. We focus on exposure–outcome relationships that can be plausibly interpreted as causal based on interdisciplinary theory and evidence, and estimate total effects conditional on an explicitly justified set of confounding variables. As well as describing our data inputs, regression analysis methods and simulation methods, we apply the model to four hypothetical income-shifting scenarios in early childhood and estimate the general magnitude of long-term public cost savings and wellbeing benefits, alongside a battery of more specific outcomes.