Selection Bias in Comparative Research: The Case of Incomplete Data Sets

Selection bias is an important but often neglected problem incomparative research. While comparative case studies pay someattention to this problem, this is less the case in broadercross-national studies, where this problem may appear throughthe way the data used are generated. The article discusses threeexamples: studies of the success of newly formed political parties,research on protest events, and recent work on ethnic conflict.In all cases the data at hand are likely to be afflicted byselection bias. Failing to take into consideration this problemleads to serious biases in the estimation of simple relationships.Empirical examples illustrate a possible solution (a variationof a Tobit model) to the problems in these cases. The articlealso discusses results of Monte Carlo simulations, illustratingunder what conditions the proposed estimation procedures leadto improved results.