According to the sample design provided by the INE, 12% of persons will be interviewed (more than 5.7 million persons).

In order to achieve good results, in the smallest municipalities, it will be necessary for the questionnaire to be completed by all inhabitants. As the size of the municipality increases, the sample decreases progressively, and in the largest municipalities, it will be sufficient to interview somewhat more than 9% of the population.

Only those dwellings that are selected completely randomly in the sample will have to respond to the census questions. In total, the residents in some 3 million dwellings will respond to the census.

The households selected must respond to:

• A basic questionnaire consisting of only 6 questions regarding the dwelling
• An individual questionnaire, with a maximum of 22 questions, for each one of the persons resident in the household.

Any person who is qualified to respond to the questionnaire may do so, provided s/he has the data on all the residents in the dwelling.

In the 2011 Census, some 3 million dwellings will be selected at random, these dwellings being distributed throughout the country.

In order to achieve good results, in the smallest municipalities, it will be necessary for the questionnaire to be completed by all inhabitants. As the size of the municipality increases, the sample decreases progressively, and in the largest municipalities, it will be sufficient to interview somewhat more than 9% of the population.

The residents in these dwellings must complete the census questionnaire.

A person may only complete the questionnaire if her/his dwelling is selected in the sample.

If participation in the census were voluntary, the sample would not be considered a reliable representation of the population, as it would only represent, and in a very uneven way, the participating group.

The questionnaires must be completed by those persons who regularly live in the dwelling that has been chosen in the sample. Therefore, if a dwelling that is not the regular residence of any person is selected to be part of the sample, then the information must not be completed. The owners of that dwelling must only respond to the census questionnaire if they have been selected in their regular dwelling. In this case, they may send notification that nobody lives in that dwelling, using the website or the telephone number free-of-charge.

In this case, you must complete the census questionnaire. The reason for this is that the INE selects a sample of dwellings, and not of persons, and the census envelope label includes the names of several of the persons who reside or have resided in the dwelling, for the purpose of enabling localisation and delivery.