Longitudinal data enable CALDER’s researchers to study the impact of various policies on individuals and schools over time. Because census files do not confine researchers to a sample selected for a specific research question, the Center’s experts can estimate the effects of policies as they emerge and target their analyses to the population(s) intended to be affected by the policy.
While experimental data is the gold standard of statistical inference, it is hard to come by, in part because the costs (both pecuniary and political) of experiments often result in small samples that may not have enough statistical power or external validity to quantify effects with any confidence. Other statistical techniques, including the quasi-experimental methods listed above, offer the potential of identifying the treatment effect in a non-experimental setting. All quasi-experimental methods benefit from the availability of longitudinal data.