Impacto del tama？o de las familias afiliadas al Seguro Popular de Salud de México, experiencia 2004-2006

objective: to compare the average size of families affiliated with popular health insurance (sps, abbrev. in spanish) and identify variables that best predict single-person affiliation. material and methods: average sizes of families in the sps are compared using 2004-2006 enrollment records and other sources. logistic models are used to identify explanatory variables for affiliation as a single-person family. results: sps families on average are composed of one member less in comparison with other sources. the logistic models indicate that the more recent the affiliation year the more probable is affiliation as a single-person family. conclusions: the smaller number of family members implies an over-financing by the sps. it is recommended to change the unit of financing to the individual to help the operational and financial sustainability of the sps over the mid- to long-term.