In urban localities, the sample of dwellings is generally divided into four panels. In contrast, for rural localities each locality belongs to only one panel. Two investigations during two consecutive quarters. After a break of two quarters there are two additional investigations during two consecutive quarters. In each quarter the sample is composed of four panels from two or three sampling years.
Interviewers visit every dwelling in the sample.
Interviews are carried out continuously each and every week for the entire three months of the survey. In residential dwellings, the interviewers interview one of the household members aged 18 and over, from whom they receive information about all members of the household. In a dwelling where there is more than one household, each household is surveyed. In urban localities, second and third interviews for a panel are usually conducted by telephone. For each of these groups a weight is calculated every quarter, being the estimated total population of that group divided by the number of cases in the sample in the same group.