CROss-National Online Survey 2 (CRONOS-2) Panel

The world’s first large scale, cross-national, probability-based input-harmonised web panel took place in 2021-23.

The CROss-National Online Survey 2 (CRONOS-2) panel was fielded in 12 countries - Austria, Belgium, Czechia, Finland, France, Hungary, Iceland, Italy, Portugal, Slovenia, Sweden and the United Kingdom - from November 2021 until March 2023.

At the end of the main ESS Round 10 (2020-22) questionnaire, respondents in each of the 12 countries were invited to participate in the online panel across six waves (only waves 1 and 2 were completed in Hungary). 

Questions for cross-national waves 1, 2, 4 and 5 were selected for inclusion following an open competition. Respondents were asked country-specific questions during waves 3 and 6 (country-specific waves), composed by ESS national teams in each country.

For the first time, a longitudinal component was added to the ESS via the CRONOS-2 (the modules on drivers of institutional trust, COVID-19 vaccination, perception of surveys, and financial wellbeing included this).

CRONOS-2 methodology

CRONOS-2 aimed to lay the foundations for a European Social Survey web panel, increasing web-interviewing capacity across Europe and developing a mature web interviewing infrastructure. It also aimed to provide the academic, research and user community with additional substantive, high-quality, comparative data to complement existing ESS data.

Harmonisation and piggy-backing

CRONOS-2 was developed following a harmonised methodological approach, maintaining survey characteristics across countries. The main aim was to prevent methodological variations amongst countries that could potentially affect measures and confound data analysis and interpretation in a comparative setting.

Regarding the recruitment process, we implemented a piggy-backing approach, using an existing survey infrastructure that followed the same harmonisation principle. The main advantages of this approach concern the maximisation of the investments of the main ‘parent’ face-to-face survey, the reduction of panel recruitment costs, and the possibility to draw on trained interviewers.

Target population 

The panel target population was adults (18+), who have access to internet (those without internet access were not invited to join the panel), living in private households in Austria, Belgium, Czechia, Finland, France, Hungary, Iceland, Italy, Portugal, Slovenia, Sweden, and the United Kingdom.

We excluded those aged 15 to 17 for reasons related to parental consent. There was no upper age limit for participation.

Sampling Frame

Participants were recruited after participating in ESS Round 10 (2020-22). This choice allowed recruitment of panel members from random probability samples. 

Information on the ESS sampling frame and sampling procedure for each country is available via the ESS Data Portal for Round 10 at (under section 'Country documentation'):

The information about the gross sample in each country can be found via the ESS Data Portal:


All CRONOS-2 panellists were offered unconditional incentives for a value of £5/€5 per wave. Source versions of email/text message survey invitations and reminders were designed by the central team and then programmed in Qualtrics and distributed simultaneously to panellists.

More information about how incentives were administered in each country, and communication to panellists, is available via the ESS Data Portal:

Data processing 

Data processing was carried out in order to produce user friendly data files. This involved data cleaning (of labels and values), ID-scrambling, implementing custom missing values, the inclusion of Admin variables for randomisation and split-ballot experiments, computation of indicator variables for survey completeness and interview duration, and making data available in multiple formats.

Due to ethical considerations, panel members were allowed to ‘skip’ any question if they wished to do so, even if they had not provided any answers. Data were checked for disclosure risks by national teams. Identification risks arose for just two variables (Wave 5: “Some people describe themselves in the same way as their sex registered at birth whereas others choose something different. How do you describe yourself?” and the following string variable “How do you describe yourself?). As those variables were judged to present a significant disclosure risk, Sikt removed them from the published datasets. The variables can be accessed under special licence be provided by Sikt.

CRONOS Prospectus

As part of the SUSTAIN-2 project, the ESS produced a Prospectus that outlines how a CROss-National Online Survey (CRONOS) may be implemented. 

The brochure includes information about CRONOS and CRONOS-2. It also explains how CRONOS-3 will be implemented as part of the Infra4NextGen Horizon Europe project.

There are sections about the methodological approach, potential costs of participation and a series of substantive and methodological findings from the implementation of CRONOS-2.


The CRONOS-2 panel was developed under Work Package 6 (WP6) 'Laying the foundations for a European Social Survey web panel' of the project ‘ESS-SUSTAIN-2’.

The project was funded by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 871063. CRONOS-2 was also supported by ESS ERIC Work Programmes (2019-21) and (2021-23).

Neither the European Commission nor ESS ERIC bears any responsibility for any use that may be made of CRONOS-2 data.

The design and implementation of the CRONOS-2 panel was centrally led and coordinated by Gianmaria Bottoni (ESS ERIC HQ) with the support of Rory Fitzgerald and Elissa Sibley (ESS ERIC HQ).

Staff at Sciences Po (Geneviève Michaud, Quentin Agren, Lothaire Epee, El hassane Gargem, Malaury Lemaître Salmon, Baptiste Rouxel, Tom Villette) provided technical support for Qualtrics and the Web Panel Sample Service (WPSS).

The team at Sikt (Linn-Merethe Rød, Benjamin Beuster) were responsible for data processing and archiving tasks. Supporting the central team in questionnaire design were Brita Dorer (GESIS), Alun Humphrey (NatCen) and Diana Zavala Rojas (UPF). Brita Dorer also coordinated the translation tasks across the participating countries. 

The central team worked closely with 12 national teams: 

  • Austria: Peter Grand (national coordinator, Institute for Advanced Studies, IHS), Marie Lisa Sailer (IHS)
  • Belgium: Bart Meuleman (national coordinator, KU Leuven, KUL) and Pierre Baudewyns (national coordinator, University of Louvain, UL), Celine Wuyts (KUL), Daniël Spruit (KUL), Stefano Camatarri (UL)
  • Czechia: Klára Plecitá (national coordinator, Czech Academy of Sciences, SAV), Jaroslava Pospíšilová (SAV)
  • Finland: Heikki Ervasti (national coordinator, University of Turku, UT), Takis Venetoklis (UT), Sami Mustikkamaa (UT), Mari Anttila (UT), Sofia Portaankorva
  • France: Agnalys Michaud (national coordinator, Sciences Po, SP), Chiao Li (SP), Brune du Marais (SP), Nicolas Sauger (SP)
  • Hungary: Vera Messing (national coordinator, Hungarian Academy of Sciences, MTA), Bence Ságvári (MTA), Gergely Hammer (MTA), Gabriella Borsós (MTA)
  • Iceland: Guðbjörg Andrea Jónsdóttir (national coordinator, University of Iceland) Árni Bragi Hjaltason (University of Iceland)
  • Italy: Sveva Balduini (national coordinator, National Institute for Public Policy Analysis, INAPP), Cristiano Vezzoni (University of Milan, UniMi), Manuela Bonacci (INAPP), Giulia Dotti Sani (UniMi)
  • Portugal: Alice Ramos (national coordinator, Institute of Social Sciences, University of Lisbon, UCS-UoL) Diogo Dinis (UCS-UoL)
  • Slovenia: Slavko Kurdija (national coordinator, University of Ljubljana, UvL) Tina Vovk (UvL), Živa Broder (UvL)
  • Sweden: Mikael Hjerm (national coordinator, Umeå University, UU), Filip Fors Connolly (UU), Katarina Östberg (UU)
  • UK: Alun Humphrey (national coordinator, NatCen Social Research), Natalie Maplethorpe (NatCen), Imogen Stevenson (NatCen)

Additional details on the design and implementation of CRONOS-2 are available via the ESS Data Portal:

CROss-National Online Survey (CRONOS) Panel

Building on previous experience of mixed mode research, the ESS developed a CROss-National Online Survey (CRONOS) panel in 2016.

CRONOS was the first attempt to establish a cross-national probability-based online panel following a harmonised approach - from the recruitment stage to data processing. CRONOS was a pilot study to evaluate the effectiveness of panel recruitment on the back of an existing cross-national survey in terms of costs, sample representativeness, participation (and attrition rates) and data quality.

CRONOS was designed and implemented alongside ESS Round 8 (2016/17), as part of the larger SERISS project. After completing the ESS face-to-face interview, respondents in Estonia, Great Britain and Slovenia aged 18 or older were invited to participate in six 20-minute online surveys over twelve months. Respondents who did not have internet access for private use were offered a tablet and an internet connection for the duration of the project.

After implementing a harmonised recruitment approach, the CRONOS panel was managed centrally with continuous and crucial support from relevant national teams. A central panel administration system was set up on Questback-EFS: waves were programmed, distributed and monitored centrally from this system. The national teams translated and adapted all source documents (respondent communications, survey questions), sent out postal and SMS communications, set up experiments and maintained a helpline that panellists could contact for assistance or queries. In addition, national teams worked with the central team in the design of recruitment strategies and experiments.

Data collection took place between December 2016 and February 2018. After a short 10-minute welcome survey, waves 1 to 6 included around 100 questions on diverse topics, often borrowed from high-standard cross-national surveys (e.g., European Values Study, Generations and Gender Programme, International Social Survey Programme, European Quality of Life Survey).


CRONOS panel data is available via the ESS Data Portal.

CRONOS methodology

The CRONOS panel also served as a platform for research on survey panel participation and question pre-testing. The research focused on incentives and contact mode experiments to enhance higher participation, experiments seeking to motivate respondents to be as accurate as possible when completing the surveys, experiments on translation approaches and numerous question wording experiments.

Research analysing the data CRONOS data is currently being undertaken by the ESS HQ. The current research primarily concerns the methodological considerations related to setting up a cross-national, probability-based online panel and the quality of the data obtained from the CRONOS achieved sample.

These ongoing studies look at:

  • The representativeness of the CRONOS achieved sample
  • Smartphone survey completion: comparing data quality for respondents who completed CRONOS surveys on a smartphone, versus those who used a desktop computer
  • Analysis of the contact mode experiments implemented in waves 5 and 6
  • The substantive impact of differential sample composition between the ESS and CRONOS
  • The substantive impact of including the offline population.


The CRONOS panel was developed under Work Package 7 (WP7) ‘A survey future online’ of the project ‘Synergies for Europe’s Research Infrastructures in the Social Sciences (SERISS)’.

The project was funded by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 654221. The CRONOS initiative was also supported by ESS ERIC Work Programmes (2015-17) and (2017-19).

Neither the European Commission nor ESS ERIC bears any responsibility for any use that may be made of CRONOS data.

The design and implementation of the CRONOS panel was centrally led and coordinated by researchers at ESS ERIC HQ (Ana Villar and Elena Sommer), the Norwegian Centre for Research Data, NSD (Didrik Finnøy, Bjørn-Ole Johannesen, and Linn-Merethe Rød), the University of Ljubljana (Nejc Berzelak), and CentERdata (Arnaud Wijnant). The central team worked closely with the three national teams.

The CRONOS national team in Estonia comprised Mare Ainsaar and Indrek Soidla (University of Tartu); in Slovenia Slavko Kurdija, Tina Vovk, May Doušak, Živa Broder and Rebeka Falle (University of Ljubljana); and in Great Britain Alun Humphrey, Emma Fenn, Matt Jonas, and Joanne Maher (NatCen Social Research).

Supporting the central and national teams were:

The CRONOS advisory board

Vasja Vehovar (University of Ljubljana), Salima Douhou (City, University of London), Anne Cornilleau (Sciences Po), Mario Callegaro (Google), and Michael Bosnjak (Leibniz Institute for Psychology and University of Trier).

Researchers at several SERISS-partner institutions

  • Gianmaria Bottoni, Alessandra Gaia, Sarah Butt, and Rory Fitzgerald at ESS ERIC HQ.
  • Erlend Aarsand, Kirstine Kolsrud and Knut Skjåk at NSD.
  • Wiebke Weber and Melanie Revilla at Universitat Pompeu Fabra.
  • Eric Balster at CentERdata.
  • Annette Scherpenzeel and Julie Korbmacher at the Munich Center for the Economics of Aging.

Additional details on the design and implementation of CRONOS can be found on the SERISS website, under Work Package 7: