Measures of state capacity: so similar, yet so different

This study provides a systematic comparative analysis of seven common cross-national measures of state capacity by focusing on three measurement issues: convergent validity, interchangeability, and case-specific disagreement. The author finds that the convergent validity of the measures is high, but the interchangeability of the measures is low. This means that even highly correlated measures of state capacity can lead to completely different statistical inferences. The cause of this puzzling finding lies in strikingly large disagreements on some of the country scores. The author shows that these disagreements depend on two factors: differences in underlying components and the level of state capacity. Considering the findings of this study, users of measures of state capacity must not assume that any highly correlated indicator is appropriate. They should instead look at what the indicators actually measure and ensure that a given definition of state capacity matches the chosen indicator.