Two countries, one happiness? The Interdependent Happiness Scale in Italy and Poland

Although Interdependent Happiness Scale (IHS) has been used in different socio-cultural contexts, no study has tested the measurement invariance across countries. Because previous research did not agree on the dimensionality of the scale, we primarily investigated the factorial structure of the IHS, comparing the one-factor model to three-factor, second-order, and bifactor models. We also evaluated the applicability of the IHS to Italian (N = 290) and Polish samples (students: N = 253; community: N = 241) using a multigroup confirmatory factor analysis. We investigated also whether the scale measures an aspect of happiness different from satisfaction with life. The bifactor model fitted the sample data better than alternative models in all samples. The general factor accounted for over 90% of the reliable variance in the total IHS score for all samples. Our study supported the configural and metric invariance of the bifactor model in the Italian and Polish versions of the IHS, ensuring the comparability of correlations involving the IHS scores in the two different cultures and samples. We showed that IHS is not redundant with the SWLS, although the two concepts are deeply intertwined. Our findings provided support for a conceptualization of interdependent happiness as a hierarchically organized construct.