Annual

The Ecmoss surveys are employer surveys. Data is collected from March to November for each year of collection (2025 for Ecmo 2024).

Establishments can answer by paper questionnaire, computer file (for large companies) or by internet via the “Coltrane” portal (for establishments with no more than 5 employees surveyed).

Establishments receive an “Establishment” questionnaire and questionnaires about one or more of their employees who are specifically named (between 1 and 24). It’s therefore employers who respond to the “Employee” questionnaires.

The Ecmo 2024 collection took place from April to October 2025.

Local unit (of an enterprise)

The sample is selected using a two-stage design, stratified at each stage. First, establishments are drawn and then employees within these establishments. The stratification used is designed to optimise the accuracy of the main indicator (hourly wages) according to the main breakdowns required by law (by sector of activity, company size, region in particular).

The sampling rate is approximately 3.2% for the establishment level and 0.9% for employees.

The Ecmoss samples are part of the negative co-ordination process between the surveys undertaken at INSEE.

Around 18,000 establishments are surveyed, representing 165,000 employees

The Ecmo 2023 questionnaires are provided in the french section

The results are analysed and compared with other indicators disseminated by INSEE, particularly in the context of the quality report sent to Eurostat.

The tables sent to Eurostat always use two successive annual surveys. They are therefore based on observations surveyed in the survey year (N) as well as observations surveyed in the year before (N-1). The earnings variables observed in year N-1 are updated ("aged") to be representative of year N.

Enrichment with administrative data

At the end of the data collection, the file of respondents is enriched with information from the ‘All employees’ database (BTS), mainly derived from administrative sources (DSN). This enrichment of information from administrative sources is central to the survey process, not only to complete the survey data, but also to check the consistency between administrative information and information from the survey and to decide to adjust where necessary.

Clearance and correction of non-response

For the ‘employee’ questionnaires:

DARES is responsible for the adjustment of the ‘employee’ questionnaires. The survey's central variables (gross salary and number of hours paid) are checked, in particular using individual data from the BTS database.

INSEE then carries out a second set of adjustments on the employee data, to comply with the constraints imposed by Eurostat. In particular, a special treatment is carried out for employees on fixed-term contracts, for whom Eurostat requires the number of hours paid to be provided.

For the ‘establishment’ questionnaires:

The adjustment of ‘establishment’ questionnaires particularly concerns the Ecmo format, where the establishment part is essential for responding to Eurostat. First of all, respondents are distinguished according to their level of response: they may in fact respond for the establishment or for the enterprise, when the information at establishment level is unknown. The establishments table is then cleared by eliminating establishments for which there is or is considered to be total non-response (i.e. establishments that do not respond to a whole block of variables or to certain so-called ‘key’ variables, such as those relating to costs or payroll). Missing or incorrectly completed responses to questions other than the ‘key’ questions which lead to the establishment being classified as totally non-responsive are adjusted by imputation, in particular by hot-deck.

Treatment of influential units

A treatment of the influential units is carried out in order to control the ‘influence’ of individuals whose response and high weighting - without their response being erroneous - lead to measurements that are still unbiased but potentially much less accurate in terms of the statistics of interest in the domains to which they belong. A winsorisation technique (Kokic and Bell's method) is therefore applied, which reduces the weight of the influential individual without losing any information about their response.

Margin calibration

For each annual survey, the variables derived from the survey are calibrated against the margins of the total population in paid employment derived from the BTS in the Ecmoss field, according to a number of criteria (social category, gender, geographical location, etc.). Margin calibration is performed using the Icarus package.