Causes and possible remedies for the “slipping seats” phenomenon: An empirical analysis

The Italian electoral laws for elections to the Chamber of Deputies and Senate enforce two key constraints: fixed seats per territorial division based on population, and fixed seats per competing lists at the highest territorial level. The electoral system aims to match elected members with both list votes and seats allocated to lower territorial levels. Complexities arise when seat allocation occurs at multiple levels, leading to theoretical challenges of proportionality. Algorithms are used to approximate proportional representation, but issues such as “slipping seats” persist, influenced by factors like varying district populations and seat allocations. Corrective measures are proposed to address this phenomenon.