Publication

This paper describes how an increasing number of studies comparing legislatures rely on analyses of roll call votes. The author explains how such analyses are used to infer characteristics on how legislatures work and how their members vote. Yet such inferences may also be problematic, if not all votes in parliament are recorded, or the recorded votes are systematically distinct from the rest of the votes. Neglecting the way in which roll call votes are triggered or decided may hence result in selection bias. The paper discusses such problems of selection bias regarding the different rules employed in legislatures and the various processes that may lead to roll call votes. The author presents evidence for various selection biases from the source of all the electronically recorded votes between 1995 and 2003 in the Swiss lower house. A careful analysis illustrates to what extent commonly used figures of party discipline are biased because of the selective nature of roll call votes. As a conclusion, the paper therefore proposes a simple but effective way for correcting such decisive biases.