Since 1995, the National Statistics Institute with the support of the MADIO Project, had run a 1-2-3 household survey system in the city of Antananarivo. It was based on an employment survey (phase 1), carried out every year, on a sample of 3000 households and approximately 15000 individuals. This survey was the basis of phase 2 (informal sector) and 3 (consumption, poverty), conducted every three years (1995, 1998, 2001), according to the survey-grafting principle. In 2000, the survey was extended to the country's 7 largest cities. Since 1997, they adopt a rotating panel method, and began renewing 1/3 of the sample each year. Sample size for the 1997-99 panel was 2676 households. Panel sample size in 2000 was 2,999 households, sample size in 2004 was 2,396 households.