In the Standard and Special Eurobarometer series and starting with survey 32, for each of the participating countries a comparison between the sample composition and a proper universe description regarding socio-demographic criteria is carried out for the preparation of post-stratification weights (also refered to as "redressment" or "unit non-response" weight). The universe description is made available by the National Research Institutes and/or by EUROSTAT. On this basis a national weighting procedure, using marginal and intercellular weighting, is applied. As such in all countries, minimum sex, age, region NUTS II (basic regions as defined by the EUROSTAT nomenclature of territorial units for statistics), and size of locality are introduced in the iteration procedure. The actual calculus is not disclosed.
The population size weighting factors correct for the fact that most countries have almost identical sample sizes (n=1000), no matter how large or small their populations are. These weights ensure that each country as well as the lower level samples (Great Britain and Northern Ireland, East and West Germany) are represented in proportion to its population size within the respective nation (United Kingdom, Germany) or in different country groupings (historical compositions of the European Union). By general rule the population size weights in the Eurobarometer include the post-stratification weighting factors as available.
A design weight (also referred to as "transformation weight") which would adjust for unequal selection probabilities due to the sample design (e.g. depending on the household size in the case of the multi-stage household sample design as used for the Eurobarometer) is not provided.
To weight or not to weight?
For descriptive statistics (uni-, bi- or multivariate) the application of the Eurobarometer POST-STRATIFICATION WEIGHTS is recommended, the application of the POPULATION SIZE WEIGHTS mandatory. Official Eurobarometer reports are based on weighted data.
For inferential statistics there is no straightforward recommendation whether or not to base the analysis on weighted data. The decison might depend on the target universe or on the statistical method. Anyway, comparing results for weighted and unweighted data could be a reasonable test.
Recommended for reading
Häder, Sabine; Gabler, Siegfried (1997): Deviations from the Population and Optimal Weights, in: Saris, Willem E.; Kaase, Mas (eds.): ZUMA Nachrichten Spezial. Band 2, Mannheim.
Arzheimer, Kai (2009): Gewichtungsvariation. In: Schoen, Harald; Rattinger, Hans; Gabriel, Oscar (Hrsg.): Vom Interview zur Analyse. Baden-Baden. S. 361-388.
Gabler, Siegfried; Ganninger, Matthias (2010): Gewichtung. In: Wolf, Christof; Best, Henning (Hrsg.): Handbuch der sozialwissenschaftlichen Datenanalyse: VS Verlag für Sozialwissenschaften, S. 143-164.
Labelling and description of the COUNTRY/NATION WEIGHTS
Up to six weights are available for the analysis of individual COUNTRIES resp. SAMPLES (East and West Germany, Great Britain and Northern Ireland) or NATIONS (United Germany and the United Kingdom).
The following description refers to Eurobarometer from wave 32 (Autumn 1989) onwards. In prior Eurobarometer weighting factors on sample or nation level have not been provided continuously for all countries and the weighting procedure might differ from the foregoing description. Information on available weighting factors up to wave 31 is compiled in a separte weighting overview (425 kB) and in the respective variable reports (codebooks).
WEIGHT RESULT FROM TARGET (W1) is a pure post-stratification weight which reproduces the real number of cases for each country. British and Northern Irish as well as East and West German samples are weighted separately. This weight is available starting with survey 34 and in its function corresponds to former NATION WEIGHT II (as available until Eurobarometer 31A). This weight assumes that all samples are analyzed separately.
WEIGHT ADJUSTED TO STANDARD SIZE is equivalent to WEIGHT RESULT FROM TARGET but adjusting all samples to the standard size of 1000 cases (respectively 300 for Northern Ireland and 500/600 for Luxembourg). For surveys 32 and 33 the 'United Kingdom' weighting factor is included. This weight is usually applied in the reports produced on behalf of the European Commission if samples are analyzed separately. This weighting factor is only available up to Eurobarometer 54.1.
WEIGHT (SPECIAL) GERMANY (W3) adjusts the East and the West German samples to their respective proportions in the united Germany and includes the respective post-stratification factors. This weight has to be applied whenever the united Germany (East+ West) is analyzed as a whole. This weight is available starting with Eurobarometer 34. Until survey 54.1 the samples are adjusted to the standard size. Starting with Eurobarometer 62 all other samples are excluded from calculation.
WEIGHT (SPECIAL) UNITED KINGDOM (W4) adjusts the British and the Northern Irish samples to their respective proportions in the United Kingdom and includes the respective post-stratification factors. It has to be applied whenever the United Kingdom is analyzed as a whole. Unlike the corresponding former NATION WEIGHT I (as available until Eurobarometer 31A) all samples up to survey 54.1 are adjusted to the standard size. Starting with Eurobarometer 62 all other samples are excluded from calculation. From Eurobarometer 89.2 onwards this weight is no longer available since from then on Northern Ireland is covered as a part of the United Kingdom sample instead of a seperate sample.
WEIGHT (SPECIAL) UNITED KINGDOM + GERMANY combines the special weighting factors for the United Kingdom and the united Germany (East+ West) for simultaneous analysis of both. This combined weight is available from Eurobarometer 47 to 61.
- Starting with Eurobarometer 76 additional auxiliary weigthing variables are included in the archive editions which correct for the population size within GERMANY and the UNITED KINGDOM without excluding the other countries (see below): WEIGHT RESULT FROM TARGET UNITED GERMANY, WEIGHT RESULT FROM TARGET UNITED KINGDOM, WEIGHT RESULT FROM TARGET NATION (United Germany and United Kingdom). These weights have been derived by the archive.
Separate post-stratification weights are available for autonomous (exceptional) participants like Norway (WEIGHT RESULT FROM TARGET NORWAY ONLY) or Candidate Countries like Finland before becoming official EU member (WEIGHT RESULT FROM TARGET FINLAND ONLY). The real number of cases are reproduced.
Labelling and description of the EU WEIGHTS
The EU WEIGHTS include the adjustments of each national sample in proportion to its share in the total population of the European Union (European Community), aged 15 and over. These adjustments are based on population figures published by EUROSTAT in the Regional Statistics Yearbook. The EUROPEAN WEIGHTs include the post-stratification sample weighting factors.
Up to more than 20 European weights are provided for use in analyses of the European Union population as a whole or in accordance with its historical compositions in the process of enlargement or of the introduction of the common currency (EURO). Unlike the former EUROPEAN WEIGHT (as available until Eurobarometer 31A) the total of samples is adjusted to the standard size up to survey 54.1. In general all samples which are not relevant (i.e. not belonging to the respective group of samples) are excluded from calculation.
WEIGHT EU 6 (W5) refers to the group of the six EC founder members France, Belgium, Netherlands, West Germany, Italy, and Luxembourg.
WEIGHT EU 9 (W6) adds the three new members as of 1973: Denmark, Ireland and the United Kingdom (Great Britain+Northern Ireland).
WEIGHT EU 10 (W7) adds Greece (enlargement 1975).
WEIGHT EU 12 (W8) refers to the group of twelve member countries after the 1986 enlargement (Spain and Portugal); after the re-unification of Germany EU WEIGHT 12+ (W9) adds East Germany starting with a separat sample in 1990 (Eurobarometer 34).
WEIGHT EU 15 (W11) in addition includes the new member states (NMS) as of the 1995 enlargement. WEIGHT EU NMS3 (W10) adjusts the populations of the three new members Austria, Sweden and Finland.
WEIGHT EU 25 (W14) refers to the group of the 25 EU member countries after the 2004 enlargement; WEIGHT EU NMS10 (W13) adjusts the populations of the ten new member countries Cyprus (Republic), Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia.
WEIGHT EU 27 (W22) adds the the two accession countries Bulgaria and Romania as of 2007; WEIGHT EU NMS12 (W24) adjusts the populations of the therewith in total 12 eastern enlargement member countries; WEIGHT ACCESSION COUNTRIES (W18) reduces the calculation to the group of these two accession countries (AC).
WEIGHT EU 29 (W16) in addition includes the remaining two candidate countries as of 2007, Turkey and Croatia; WEIGHT CANDIDATE COUNTRIES (W19) reduces the calculation to the group of these two candidate countries (CC); WEIGHT AC/CC (W15) adjusts the populations of the four accession and candidate countries as a group.
Particular EUROPEAN WEIGHTS may include one or more additional countries which are intermittently surveyed in recent Eurobarometers: Macedonia, the Turkish Cypriote Community (TCC) or any of the EFTA countries, as indicated in each case.
WEIGHT TOTAL (total n of all participating countries) adjusts the populations of ALL participating samples as a group. This weight should only be applied all participating countries (=samples) are to be analyzed in total.
WEIGHT (SPECIAL) EURO ZONE separates the group of eleven countries which accepted to introduce the EURO (Common European Currency), as of 1999 (Belgium, Germany, Spain, France, Ireland, Italy, Luxembourg, the Netherlands, Austria, Portugal and Finland) from the non-EURO countries (EB 49 to 59.1). Starting with Eurobarometer 54.0 an (additional) EURO ZONE weight includes Greece in the group of countries which adopted the EURO as of 2001. WEIGHT SPECIAL EURO ZONE 13 adds Slovenia (2007), WEIGHT SPECIAL EURO ZONE 15 (W29/W30) in addition covers the Republic of Cyprus and Malta (2008), WEIGHT SPECIAL EURO ZONE 16 (W81/W82) adds Slovakia (2009), WEIGHT SPECIAL EURO ZONE 17 (W89/W90) adds the new EURO zone member Estonia (2011).
WEIGHT (SPECIAL) NON-EURO ZONE (W30/W82/W90) reduces the calculation to the group of the respective non-EURO, but EU member countries.
WEIGHT EFTA (W17) refers to the group of the three EFTA countries Iceland, Norway and Switzerland, if available in the particular survey.
OVERSAMPLES are weighted separately as documented in the respective codebooks / variable description or in the technical specifications.
WEIGHT EXTRAPOLATED POPULATION 15+ (wex) extrapolates the actual universe (population aged 15 or more) for each country/sample, i.e. this weight variable integrates all other available weights, but does not reproduce the number of cases in the data set, but projects the survey results onto universe figures. This weight is available from Eurobarometer 66.2 onwards.
Patch: DE/UK WEIGHT
For analysing united GERMANY and the UNITED KINGDOM, each or both as a whole, and keeping all other countries, you might need to run a patch syntax which produces the adequate COUNTRY and (post-stratification + population size) WEIGHT variables. [Instruction+syntax (200 kB)] [SPSS syntax (3,78 kB)] [Stata syntax (3,95 kB)].
From Eurobarometer 89.2 onwards there is no separate Northern Ireland sample. For those Eurobarometers we therefore provide an updated patch [SPSS syntax (1,59 kB)] [Stata syntax (1,67 kB)] that merges the two separate German samples only.
Dataset Archive Editions published from 2014 onwards will usually already include these auxiliary variables. Up to Eurobarometer 61 appropriate variables were regularly provided by the data producer.