Single-party dominance became widely-spreaded around the world. Single-party dominance is described as a long control over power by same party through regular winning elections. I consider all ended cases of single-party dominance in the world on national level in 1950-2014. The sample includes cases of single-party dominance in both democratic and electoral authoritarian regimes. Effective number of parties (ENP) shows a level of electoral competition. ENP is calculated on Laakso and Taagepera method as an average number for all elections (presidential or parliamentary – depend on executive type selection) during a period of single-party dominance. If government establishes as a result of presidential election - ENP is calculated for presidential election and if government establishes as a result of parliamentary election - ENP is calculated for parliamentary elections. Durability of single-party dominance is described as a time (number of months) that dominant party controls executive power. The objective of the research is to reveal, has ENP influence longevity of dominant party regime. Hypothesis is that ENP positively correlates with durability of single-party dominance. The method of the research is correlation analysis. Independent variable is average ENP for presidential or parliamentary elections. Dependent variable – length of single-party dominance (months). The main conclusion of the research is that ENP has a positive effect on durability of single-party dominance.
