The WHO-5 Well-Being Index – Testing measurement invariance across 33 countries

In recent years, several studies have stressed out the importance to guarantee the comparability of theoretical constructs (i.e. measurement invariance) in the compared units (e.g., groups or time points) in order to conduct comparative analyses (e.g. Harkness, Van de Vijver, & Mohler, 2003; Meredith, 1993; Vandenberg, & Lance, 2000). If one does not test for measurement invariance (MI) or ignores lack of invariance, differences between groups in the latent constructs cannot be unambiguously attributed to ‘real’ differences or to differences in the measurement attributes. The five-item World Health Organization Well-Being Index (WHO-5) is a frequently used brief standard measure in cross-cultural large-scale clinical studies (Topp, Østergaard, Søndergaard, & Bech, 2015). However, MI as a prerequisite for cross-country comparisons remains untested to date.
We performed multigroup confirmatory factor analyses (MGCFA) and the alignment method (Asparouhov & Muthén, 2014) to test the WHO-5 for MI across 33 countries and for cross-time MI over five years. Analyses were based on data of the 2010 and 2015 waves from the European Working Condition survey (EWCS). The EWCS collected data via computer-aided personal interviews in a sample of 41,870 employees and self-employed individuals (wave 2010; wave 2015: 41,290) from the EU28 countries as well as Norway, Switzerland, Albania, the former Yugoslav Republic of Macedonia, Montenegro, Serbia and Turkey.
MGCFA indicated metric MI and lack of scalar MI of the WHO-5. The alignment method revealed several non-invariant parameters across countries. We estimated latent mean differences between countries with the scalar and the alignment method.
The results corroborate the need to use latent variable modeling and to account for non-invariant parameters when mean levels are of concern. Furthermore, the poor performance of some items in some countries has to be considered.