EQLS 2007 - Methodology

In preparation for the Second EQLS a review of methodology used in the 2003 survey was carried out and recommendations for improvement are reflected in the second survey.

In the second European Quality of Life Survey, the fieldwork was carried out from 20  September and finished, in most countries, on 20 November 2007. The fieldwork in Denmark was completed on 13  December 2007 and in Luxembourg on 18  January 2008. The only exception was FYR Macedonia where the fieldwork was conducted in February 2008, because this country was added to the survey at a later stage.

Interviews

The overall response rate was 57.9% which was calculated as the proportion of completed interviews from the net sample (gross sample less the non contacts of all kinds). However, there are significant country variations in response rates ranging from 88% in Romania to 33,5% in the UK. The same method of calculating the response rate was used in the 2003 survey (58,4% response rate).

Response rate

Sample design

The sample of the European Quality of Life Survey is representative of the adult persons who were living in private households during the fieldwork period in each of the countries covered.

In most of the countries, the EQLS sample followed a multi-stage, stratified and clustered design with a ‘random walk’ procedure for the selection of the households at the last stage (with the exception of Netherlands, Sweden and Norway where the selection of the respondents was made using phone registers and Malta and Belgium where all respondents were randomly selected from the population register). 

The sampling selection process was random at each stage, i.e. the selection of primary sampling units, the selection of addresses, the selection of households and the selection of individuals aged 18 and over. Only one person from the same household was interviewed.

Sample size

The target number of interviews was 1,000 in most countries although the larger countries had bigger sample targets: 1,500 interviews in Poland, Italy, France and the UK, and 2,000 interviews in Turkey and Germany. The target sample size and number of interviews actually carried out in each country is summarised in the following table.

Table: Completed interviews

In order to ensure that the results of the second European Quality of Life Survey are representative, three types of weighting have been applied to the data:

• Design weights. The data is weighted in order to account for the unequal probability of selection of respondents. This compensates for the fact that, in a one-person household, the probability of being selected is 100%, whereas it falls to 33% in a three-adult person household.
• Non-response weight. This weight corrects for possible biased estimations arising from different types of eligible respondents which have different response rates. In this stage the variables taken into consideration in the weighting procedure are age, gender, urbanisation level, region (NUTS 2 or corresponding national regional classification), household size (adults in size of household).
• International weights. this final step in the weighting is applied in order to be able to generate estimations for groupings of countries (EU27, EU15, NMS12, CC3). The weights of all respondents in each country are multiplied by the proportion that this country represents in the total adult population in the respective cross-national area. This removes the bias that occurs due to a proportionally greater number of interviews in smaller countries. For international weighting, the official population figures provided by Eurostat or national statistic offices are used.

The quality of the  survey processes was assessed in all its stages, starting from the sampling design to the final dissemination of data.

The quality assessment report also assessed the quality of the survey output on the following five key quality components set out by the European Statistical System: Relevance, Accuracy, Timeliness, Accessibility and clarity and Coherency and comparability. On the basis of the assessment it makes recommendations for the forthcoming rounds of the survey.