“…Ex-post harmonisation (henceforth, harmonisation) aims to merge data from different survey projects into a unified analysis-ready dataset, even if the original data were not intended for recycling (Granda et al 2010). While complete cross-project data harmonisation is typically only possible for socio-demographic variables (Hoffmeyer-Zlotnik and Wolf 2003), it remains partially possible for narrow and specific issues, e.g., corruption (Wysmułek 2019), democratic values and protest behaviours (Słomczyński et al 2016), European integration (Jabkowski and Cichocki 2022), general social trust (Bekkers et al 2018), health lifestyles (VanHeuvelen and VanHeuvelen 2021) or national identities and religion (Bechert et al 2020). In contrast to socio-demographic characteristics, cross-project harmonisation of substantive survey questions faces acute measurement problems.…”