Research project The Nordic countries, through the availability of administrative and health registers (and the possibility to link them for research purposes), have world unique infrastructures to perform observational studies. The purpose of such studies is often to evaluate the effect of a causal variable on an outcome of interest, such as the effect of a labor market program on time in unemployment or the effect of adult education on time of retirement.
In such studies there is a need to control for background variables (eg, education, income, gender) that affect both the causal agent and the outcome of interest. In this context, non-parametric methods are increasingly used because they require few model assumptions. The latter flexibility is important in studies where many individuals are observed which is common in the case of observational studies. The purpose of this project is to develop and study methods for selecting background variables and to study properties of nonparametric estimators of causal parameters when this and other necessary model choices are taken into consideration. The project results are expected to be relevant for researchers involved in register based research and the methods are intended to be implemented in freely available software, making flexible estimation of causal effects more accessible to practioners.