General information
| Contractor | Ipsos NV, Belgium |
| Coverage | EU Member States, Albania, Bosnia and Herzegovina, Kosovo, North Macedonia, Montenegro, Serbia, and Norway, Switzerland, and the United Kingdom |
| Fieldwork period | March–November 2021 |
| Target population | All residents of the countries mentioned above aged 16 or older and in employment at the time of the survey. People were considered to be in employment if they had worked for pay or profit for at least an hour in the week preceding the interview (ILO definition). |
| Sample | Random probability sampling was used to generate nationally representative samples for each country. Random direct dialing to mobile telephones was used for all countries except Sweden, where both mobile and landlines from a population register were used. |
| Sample size | The smallest sample size foreseen was 1,000 (potential and candidate countries and Switzerland), and the largest was 4,100 (Germany); in most countries, the expected sample size was 1,800. Variations were due to budget availability, size of the workforce, or top-ups by individual Member States. The final number of interviews achieved after quality control in all 36 countries was 71,758. |
| Type of interview | Telephone interview, median duration of 22 minutes. |
For more information, see the Technical Report.
Sampling
The sample used in the European Working Conditions Telephone Survey (EWCTS) 2021 is representative of those aged 16 years and over who are in employment and are resident in the country that is being surveyed. In 35 of the 36 countries, a single-stage, un-clustered sampling design was used. The kind of design employed is known as Random Digit Dialling (RDD), which implies that a computer randomly generates telephone numbers that match the configuration of telephone numbers in a country.
About the sampling procedure
The sampling frame used was mobile phones with numbers randomly generated with equal probability. These numbers were screened to remove those on ‘do not call’ lists, as well as inactive numbers or numbers for which it was clear the associated telephone was not in the country. This approach results in all sampling units having an equal probability of being selected with an estimated coverage of around 95% of the population.
In Sweden, the sample was drawn from the official register of resident persons, and was stratified by municipality, age and sex. Telephone numbers (which could be landline or mobile) were then added to this sample with a 99% match rate.
In each call, a number of screening questions were asked to confirm whether the respondent was eligible before beginning the interview.
Target sample sizes by country
For most EU countries, the target was 1,800 interviews. The exceptions were for the smallest and largest countries: Cyprus, Luxembourg and Malta (1,300 interviews); Poland and Spain (2,900), Italy (3,100), France (3,200) and Germany (4,100). Two countries also made use of the possibility to pay for a boosted sample which increased the national target, namely Belgium (3,000) and Slovenia (2,622).
Among non-EU countries, the six candidate and potential candidate (CPC) countries each had a target of 1,000 completed interviews, while the United Kingdom’s target was 2,100. Switzerland and Norway, which participated in the EWCTS at their own cost, had targets of 1,100 and 3,295 interviews respectively.
Across all countries, the total target was 68,817 and by the end of fieldwork the final number of interviews achieved after quality control was 71,758.
Detailed information on the sampling procedures can be found in the Sampling and weighting report.
Coding
The EWCTS carried out in 2021 collected detailed information from respondents on occupation, economic activity, education level and geo-classification.
Coding methods
Information regarding the respondent’s occupation was recorded through two open-ended questions which were then coded into the ISCO classification of occupations, version 08, at 4-digit level. A similar procedure was applied to collect information on the sector which was coded at 3-digit level using the classification of sectors of activity, NACE 08 Rev 2. In order to protect the identity of the respondent, the microdata made available to the general public provide information at ISCO 2-digit and NACE 1-digit level.
The question that collected the respondent’s level of education also required some coding work, which was fully integrated into the data collection script. The education categories in the questionnaire were country-specific (that is, based on the local education system), so the responses were recoded in order to obtain the internationally comparable International Standard Classification of Education (ISCED) categories.
The location of respondents, in terms of the regional (NUTS) classification level and degree of urbanisation, was also collected through a separate geo-classification module. This information was then automatically coded to the corresponding NUTS levels.
Quality of the coding
Quality control measures were implemented during the entire process to ensure high-quality coding. Extensive training was provided to interviewers and coders to help them collect the most accurate information that would allow coding at the desired level. In particular, a note was provided to interviewers to guide them on how to capture high-quality information on occupation and industry, two key variables of the EWCTS.
For more detailed information on each of the classifications and the associated coding processes, please see the Coding report (forthcoming).
Weighting
Weighting is applied to survey data in order to improve the accuracy of survey estimates. To ensure that the results of the EWCTS 2021 could be considered representative of workers in the European countries covered, weighting was carried out on the data. It was necessary to apply weighting for two main reasons: first, due to the voluntary nature of the EWCTS 2021, participation may be affected by unequal response rates for different groups of people with the sampling design of Random Digit Dialling (RDD); second, workers with several mobile phones can have a greater likelihood of participating.
The weighting was conducted in two main steps – through calculating design weights and non-response adjustments.
Design weights
In the countries using RDD, because the generated sample is a list of mobile phone numbers rather than people, workers with more than one mobile phone are overrepresented. It is not possible to tell which numbers are affected until the interview, when the respondent is asked how many mobile phone numbers they have.
To account for this factor an adjustment is made, giving a smaller weight to respondents with more phones. Apart from this, within each country all mobile phones have the same likelihood of selection.
Non-response adjustments
A well-known phenomenon in surveys is that certain types of people are easier to contact or more willing to respond. To account for this, non-response adjustments are applied which gives a larger weight to groups which are underrepresented while assigning a smaller weight to overrepresented groups.
Whether a group is overrepresented or underrepresented is determined by comparing the distributions of the EWCTS respondents with the distributions found in Eurostat’s Labour Force Survey employment statistics on age, sex, occupation, sector and region of residence of the respondent. The method used is known as calibration weighting and is applied for each country separately. Numerous checks are made to ensure the quality of the weights.
Final weights
The design weights and non-response adjustments are combined to obtain the final weights. The final weights are constructed as frequency weights and indicate the estimated number of workers represented by each respondent. The weights of all the respondents in a given country add up to the total number of people in employment. They can be used both for country-level analyses or at the European level.
Detailed information on the sampling procedures can be found in the Sampling and weighting report.
Data validation
Data validity checks carried out during and after data collection for Eurofound’s surveys are an important aspect of quality control. For the European Working Conditions Telephone Survey (EWCTS), Eurofound developed a comprehensive data checking and validation exercise in collaboration with the survey contractor Ipsos.
Quality and consistency of variables
The dataset has been assessed to ensure high quality and consistency of variables, with checks covering the following:
- Routing – if respondents answered questions applicable to them according to the questionnaire script
- Permitted values – if all answers are in line with the options or combinations available for selection by the interviewer (for closed answer questions) or a permitted range of responses (for open-ended questions)
- Consistency checks – evaluating the levels of consistency between the questions when the permitted values for the particular variables were further filtered down by answers from the previous question
- Outliers –checks were designed so that any unsatisfactory values were flagged before any data analysis was completed
- Contact data validation – assessing if all contact rules have been respected
- Variables distribution and outliers – the probability/accuracy of the information provided and solutions to fix any issues found
Reporting on validation of data
For more details and the solutions applied to any issues encountered during the data validation process, please see the Data validation report.
Quality assurance
In carrying out its surveys, Eurofound places a strong emphasis on quality and aims for precision of estimates for the European Union as a whole, as well as for individual Member States. To ensure a high quality of data in the European Working Conditions Telephone Survey (EWCTS), Eurofound applied state-of-the-art practices in cross-cultural survey methodology.
Quality control measures
Each stage of the survey was carefully planned, closely monitored and documented, and specific controls were put in place. Quality control mechanisms were applied to ensure quality in terms of relevance, accuracy, timeliness and punctuality, accessibility and clarity, and coherence and comparability.
At the start of the preparation phase, the survey contractor Ipsos and Eurofound established quality assurance indicators which were outlined in an agreed Quality Assurance Plan. Each stage of the EWCTS was documented in detail in order to promote transparency and to be able to draw lessons for future surveys. As part of this process, 134 quality assurance indicators were established and their performance assessed.
Reporting on quality control
The Quality assurance and control report, compiled by Ipsos, provides a summary of the quality control activities performed before, during and after the fieldwork. The report provides an objective quality assessment of the outputs and processes against the Quality Assurance Framework. It also provides a critical reflection on the quality indicators and targets as identified in the Quality Assurance Plan.
International standards
As a further measure, Eurofound is contracting an independent third party to assess the survey quality in relation to comparable surveys and international standards, such as the quality criteria outlined in the European Statistical System, and to provide suggestions for improvement of future editions of the EWCS. The report on this exercise will be available towards the end of 2023.