The CRONOS panel (also known as the Opinion Study) is a probability-based, harmonized web panel survey project, developed as a follow-up to the European Social Survey (ESS). Coordinated by ESS ERIC, the project aims to test and enhance Europe's capacity to collect comparable data through online, multi-wave surveys across countries.

This project has been set up in 12 countries: Austria, Belgium, Finland, France, Great Britain, Hungary, Italy, Iceland, Netherlands, Portugal, Czech Republic and Serbia. It follows on from an initial project called CRONOS 1 conducted between 2016 and 2018 in three countries: the UK, Slovenia, and Estonia.

Building on this initial experience, a second panel was launched in 2021: CRONOS2 / Opinion Study, across 12 countries: Austria, Belgium, Finland, France, Hungary, Iceland, Italy, the Netherlands, Portugal, Czech Republic, Serbia, and the United Kingdom.
This project aimed to test the effectiveness of web-based data collection on a larger scale and across a more diverse range of national contexts.
Between 2021 and 2023, six waves of data collection were conducted.

In 2024, CRONOS3 was launched across 11 countries: Austria, Belgium, Czech Republic, Finland, France, Hungary, Iceland, Poland, Portugal, Slovenia, and the United Kingdom. It is the first probability-based, harmonized, and mixed-mode panel survey (web and paper) that also includes populations without internet access. CRONOS3 is structured around five waves, with content focused on the key themes of NextGenEU: Make it Green, Make it Digital, Make it Healthy, Make it Strong, Make it Equal.

Methodological contributions

At a time when it is increasingly difficult to conduct in-person surveys (cost, changes in habits post-pandemic, etc.), the CRONOS-2/Opinion Study project explores alternatives to the face-to-face method of collecting data. In particular, it seeks to assess the effects of a “mixed mode” (i.e. surveys conducted in parallel online and face-to-face) with respect to a set of criteria such as participation rates, sample representativeness, data quality and the costs of conducting surveys.

This project provides a way for all the participating institutions and members of ESS-ERIC to gain more experience experience of survey practice via an alternative to the face-to-face mode, while maintaining the most rigorous methodological standards.

This panel relies on the sample management application WPSS designed and put into operation by CDSP.

Methodology

The panellists in the CRONOS 2/Opinion Study project were recruited following the tenth round of the European Social Survey (ESS). The sample used to recruit the participants was drawn randomly. The questions and topics tackled by CRONOS-2 were obtained through an initial Europewide call for projects, from which a final selection was made by ESS-ERIC and the participating countries.

CRONOS-2/Opinion Study uses the TRAPD (Translation Review Adjudication Pretest Documentation) method for the translation of the questionnaires, to ensure that the data are comparable from one country to another.

Likewise, the protocol used to contact the panellists is the same in all the participating countries. Each panellist receives 5 euros without conditions following each new wave of the survey.

In all, one preliminary survey and six full rounds of surveys have been carried out for the CRONOS-2/Opinion Study project since 2021. Four of the full surveys and the preliminary survey are common to all the countries taking part in the project. Calls for projects were issued for these surveys, then the final selection was made by ESS-ERIC and the participating countries. They ask the panellists about a wide range of subjects relevant to them, such as well-being, values and beliefs, religion, work, living conditions and family structure, consumption, the environment.

The two remaining rounds of surveys are decided by the individual countries.

French National Data

In France, the CRONOS2 panel was composed of respondents from the ESS Round 10. A total of 1,023 panelists were recruited. Around 70% participated in each wave, representing approximately 35% of the national ESS sample. The six waves were conducted between November 2021 and March 2023.

The CDSP implemented a reinforced contact protocol: postal invitations, email and SMS reminders, phone calls, and respondent support. The surveys covered a wide range of topics, including electoral participation (2022 elections), climate, inequalities, and trust in institutions (such as universities, scientists, and fellow citizens).

The CRONOS3 panel follows a similar approach, with an expanded sample including respondents from ESS Round 11. A total of 1,709 panelists were recruited for this third edition. Fieldwork operations in France are coordinated by the CDSP. The first five waves (carried out between September 2024 and June 2025) achieved an average response rate of 60% per wave.

Data Access

Data from the first six waves of CRONOS2, along with full methodological documentation, are freely available on the ESS website.

CRONOS3 data are being progressively released starting in 2025.
Link: https://ess.sikt.no/en/series/655615e6-8e4f-4e84-a9c9-27d24b93f866

CRONOS 4 & 5 – The SoGreen Panel

Starting in late 2025, the CRONOS panel will evolve into SoGreen – Social Aspects of the Green Transition, a project coordinated by SHARE-ERIC and bringing together four major European social science infrastructures: ESS ERIC, GGP, GUIDE, and SHARE. Funded by the European Commission, SoGreen aims to examine the social impact of the green transition across different generations and socio-economic groups in Europe.

Within this framework, three new survey waves will be carried out via the CRONOS panel, using a mixed-mode approach (web and paper) in 11 countries: Austria, Belgium, Czech Republic, Finland, France, Hungary, Iceland, Poland, Portugal, Slovenia, and the United Kingdom.

The questionnaires will focus on topics related to the European Green Deal, with a set of harmonized questions enabling longitudinal analysis.

Funding