It seeks to avoid double counting active contributors who contribute to more than one scheme. This right to income security after retirement is guaranteed by the prior payment of premiums or contributions, i.e., before the occurrence of the insured contingency. Depending on the country, this prior payment of a premium or contributions concerns persons in employment or a sub- group. Combined with other indicators of security of employment, contribution to social security forms part of the set of criteria suggested to define formal employment.