The rate of incarcerated persons per 100,000 population is a widely used measure in historical and cross-national comparisons. This approach can be questioned on the ground of theoretical and political usefulness. It is apparent that the development of judicial sentencing practices has led to a complexity which is no longer grasped by an index such as imprisonment rates; however, there may be research topics which could be analyzed by the use of an index like the number of prisoners per 100,000 population. The worldwide comparative study of the relationship between unemployment and the use of penal law may be an example. Still, even this type of research should consider that many alternatives to lengthy prison terms have been developed in the last decades in many countries, so that it seems more appropriate to use more complex types of indices. Research must measure the composition of the ensemble of legal sanctions as well as the functional relations between those sanctions. The analysis focuses on the degree of homogeneity of social control. To examine this, the study discusses the historical type of comparative research and then cross-national studies. Finally, a device is suggested which may permit a more valid type of comparative research on penal sanctions. Twenty-two references are provided.