Interviewing all usual residents of Lithuania every time a statistical survey has to be conducted would be very complicated and expensive. Individuals are sampled for a survey from the Population Register, using statistical random sampling methods. Usually, one individual is interviewed only once; however, in certain surveys, an individual may be interviewed several times.
In statistical surveys on agriculture, respondents having large crop areas, growing many farm animals or poultry may be included in a sample every year. A respondent may be repeatedly sampled for several surveys.