[ENCOPREVENIMSS 2003, 2004 and 2005. 1. Methodology and studied population]

In order to assess the progress of preventive health programs by measuring the coverage and other health indicators, ENCOPREVENIMSS (Health National Surveys) 2003, 2004 and 2005 were carried out. These surveys were applied nationwide to population affiliated to the Mexican Institute of Social Security, and were representative at a state level. The sampling frame was stratified, with several stages, by clusters, and had a minimum sample of 328 people per program group in each delegation. The applied questionnaires were previously designed and evaluated through a pilot test. They included specific questions for each program component per age group. In 2004, two sections were added, based on validated instruments to evaluate frequency of food intake and physical activity. A total of 79,797 people were surveyed: 117,884 in 2004, and 122,380 in 2005. A third of the population was insured, while the rest was beneficiary; about half the population was between 20 and 59 years old, and the proportion of people older than 60 increased almost 2% from 2003 to 2005. More than 90% of those who claimed to have a paid job were factory workers or employees. More than 90% of the population were assigned to a family physician in all the assessed years. The information obtained from ENCOPREVENIMSS is a valuable tool to conduct institutional policies for public health.