Working papers results

2008 - n° 6
Propensity Score Matching (PSM) has become a popular approach to estimation of causal effects. It relies on the assumption that selection into a treatment can be explained purely in terms of observable characteristics (the unconfoundedness assumption) and on the property that balancing on the propensity score is equivalent to balancing on the observed covariates. Several applications in social sciences are characterized by a hierarchical structure of data: units at the first level (e.g., individuals) clustered into groups (e.g., provinces). In this paper we explore the use of multilevel models for the estimation of the propensity score for such hierarchical data when one or more relevant cluster-level variables is unobserved. We compare this approach with alternative ones, like a single level model with cluster dummies. By using Monte Carlo evidence we show that multilevel specifications usually achieve reasonably good balancing in cluster level unobserved covariates and consequently reduce the omitted variable bias. This is also the case for the dummy model.
Bruno Arpino, Fabrizia Mealli
Keywords: propensity score,multilevel studies,unconfoundedness,causal inference
2008 - n° 5
More educated parents are observed to have better educated children. Researchers trying to control for unobserved ability have found conflicting results: in most cases, they have found a strong positive paternal effect but a negligible maternal effect. In this paper, I use a population of twins from Norwegian Register data and evaluate the impact on the robustness of the estimates of the characteristics of the samples commonly used in this strand of research: samples of small size, with low variability in parental education, not randomly selected from the population. The part of the educational distribution involved in any identification strategy seems to be the key aspect to take into account to reconcile previous results from the literature.
Chiara Pronzato
Keywords: intergenerational transmission,education,twin-estimator,sibling-estimator,power of the test
2008 - n° 4
Using age specific fertility rates of Italian and Swedish women aged between 15 and 49 years old I examine the presence of fertility postponement in period and cohort outputs. Period data consist of standard five-year age group rates ranging from 1960 to 2005. Cohort data are arranged on age specific year groups born between years 1930-1970. The method used in this work is based upon quadratic spline interpolation procedure, developed by Carl P. Schmertmann (2003), in which three index ages determine the schedules shape. The recent fertility postponing behavior is investigated through the help of five index ages, which show the dynamics of postponement both in cohort and period data.
Alessandra Carioli
Keywords: Second Demographic Transition,fertility trends,postponement,quadratic spline interpolation,Italy,Sweden
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