KRX-0401 The selection of the groups and the municipalities is Inhibitors,Modulators,Libraries based on a method that combines probability proportional Inhibitors,Modulators,Libraries to size (PPS) sampling and systematic sampling. First the number of interviews to be realised in every province is divided by 50 to define the number of groups. The next step involves the ranking of all municipalities according to their population size in every province. A stepwise selection of municipalities is applied using the total population in every province divided by the number of groups as a step size. By doing so, big cities as well as small municipalities can be selected for the survey. In some large cities several groups can be selected. Given the dynamic nature of the NPR, the data-collection phase is split in four quarters and the quarterly samples do not involve replacement.

As a consequence, the number of people to be sampled each quarter per group was (on average) 12.5 individuals. Within each group, households were selected via a systematic sampling procedure: the population registers of the selected municipalities were ordered in terms of statistical sectors (wards), size of the households (1, 2, 3, 4, 4+ members) and the age of the reference person of the Inhibitors,Modulators,Libraries household (it is the administrative contact point of a household). The number of households to be selected is determined by dividing 12.5 by the mean household-size in every selected municipality. The total number of households of a selected municipality, divided by the number of households to be selected for the survey in this municipality, provides the selection step.

The last step in the selection process is to identify the members of the households that will be invited to participate. To avoid intra-household correlation Inhibitors,Modulators,Libraries and to limit the burden for the households, maximum four household members are selected to participate in the survey. In households with more than 4 members, the reference person Inhibitors,Modulators,Libraries and his/her partner are always selected Entinostat together with two or three other members of the household who have their birthday coming up first after the interview. An important goal of the BHIS is the assessment of time trends. Therefore no important methodological changes have been introduced since the first survey. However, two refinements in the survey methodology were applied after 1997: the possibility of oversampling of specific population groups and the geographical division of municipalities with more than one selected group.

These changes have no impact on the main methodological approach of the survey. Based on the request of the commissioners, a provincial oversampling was initiated in 2001 to offer provincial health authorities the opportunity to obtain more precise results for their province. The oversampling is subject to payment and the implementation is straightforward.