Since 1 January 2013, 858 NSR sample municipalities were identified and added to the 176 SR municipalities to define a total sample of 1,034 municipalities. In 2022 the sample size is reduced to 1,032 municipalities. The 166 SR (self-representing units) includes provincial capitals and municipalities of at least 50,000 inhabitants
The remaining 866 municipalities NSR (non-self-representing municipalities), randomly chosen according to a probabilistic design, are layered in 20 groups and the layers are defined by four geographic divisions (North-West, North-East, Centre, South) and population grouped in five classes.
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