Ethnic or immigrant minorities are considered as ‘hard-to-reach’ groups in surveys. They are relatively small in number compared to the total population, spread across the country and there tend to be no sampling frame as reference for selection of respondents from the target groups (i.e. list of people that can be used to make a controlled representative selection of the target group). This means that achieving a representative sample is more difficult compared with general population surveys.
EU-MIDIS II mainly used a multistage random probability sampling design.
Whenever possible, a sample was drawn from a sampling frame covering the target population. However, the opportunities to sample the target population are hugely different across Member States due to different availability of sampling frames and distribution of the target group in the countries.
Advanced and new sampling methodologies had to be developed and used in most countries, and the best possible design was chosen for each target group in each country. For some target groups in some countries, a combination of different methods was used to ensure better coverage of the target population. A detailed description of sampling methods used in the survey is available in the technical report.
In some countries, national coverage had to be reduced for reasons of efficiency. This means that in multi-stage sampling, areas with lower densities of the target populations of were excluded because screening of the target populations would not have been possible. The thresholds vary from areas with fewer than 2.7% in Cyprus to the 30% in Estonia. These cut-off points, which were unavoidable due to the need for screening respondents in most countries, limited the overall coverage of the target population in the countries. The median coverage across countries and target groups was 60% of the target population.