20. 12. 91 Official Journal of the European Communities No L 351/1 (Acts whose publication is obligatory) COUNCIL REGULATION (EEC) No 3711/91 of 16 December 1991 on the organization of an annual labour force sample survey in the Community THE COUNCIL OF THE EUROPEAN COMMUNITIES, Having regard to the Treaty establishing the European Economic Community, and in particular Article 213 thereof, Having regard to the draft Regulation submitted by the Commission, Whereas, in order to carry out the tasks which are assigned to it by the Treaty, and in particular by Articles 2,92, 117, 118, 122, 123 and 130d thereof, the Commis- sion must be acquainted with the situation and develop- ments in employment and unemployment ;" Whereas the advent of the internal market increases the need for statistical information on the development of economic and social  convergence so  that comparisons may be made between Member States and regions in the Community; Whereas the best method of ascertaining the level and structure of employment and unemployment consists in carrying out a harmonized and synchronized Community labour force sample survey, as has been done annually in the past, HAS ADOPTED THIS REGULATION : Article 1 Frequency of the survey In the spring of each year, starting in 1992, the Statistical Office of the European Communities, hereinafter called ‘Burostat’, shall conduct for the Commission a labour force sample survey in the Community, hereinafter referred to as ‘survey’. Article 2 Survey units 1. The survey shall be carried out in each Member State in a sample of households of persons residing in the territory of that State at the time of the survey. Member States shall make every effort to prevent double counting of persons with more than one residence. v2. The information shall be collected for each member of the households included in the sample. In cases where one member of the household provides information for other members, this shall be clearly indi- cated. Article 3 Representativeness of the sample 1. The national statistical offices shall carry out the survey within the framework of national surveys and shall ensure that the sample of households referred to in Article 2 (1) corresponds to that usually adopted in the Member State in question, in such a way that the volume of the sample will be identical to that in the national survey. 2. In this context, to ensure a reliable foundation for comparative analysis at Community level, as well as at the level of the Member States and of specific regions, the sampling plan shall guarantee that for characteristics re- lating to 5 % of the population of working age the rela- tive standard error at NUTS II level (or equivalent) does not exceed 8 %, assuming the design effect for the vari- able ‘unemployment’. Regions with less than 300000 inhabitants shall be exempt from this requirement. 3. The national statistical offices shall take the neces- sary measures to ensure that at least a quarter of the survey units are taken from the preceding survey and that at least a quarter shall form part of a subsequent survey. These two groups shall be identified by a code. 4.  Member States shall provide Eurostat with whatever information is required for the organization and meth- odology of the survey and, in particular, shall indicate the criteria adopted for the design and extent of the sample.