Patients and sampling: The study population has been distributed in groups according to age (20-34; 35-49; 50-79 years) and sex. The participants will be selected through a random, representative sample using our two-stage conglomerate sampling with stratification of the First-Stage Units. These FSUs are made up by the Basic Health Areas (Health Centers). The Second-Stage Units are made up by the individuals. The stratification criteria used in the first stage will be the socioeconomic status-rural/urban environment. The selection of sample elements will be carried out through simple random sampling from the healthcare card database pertaining to the selected Health Centers. A sequence of random, computer-generated numbers will be obtained.