The Chinese Version of the Couples Satisfaction Index: Psychometric Assessment and Differential Item Functioning Analysis with Item Response Theory

The Couples Satisfaction Index (CSI) is one of the most widely used instruments to assess intimate relationship satisfaction and status. However, its performance in the Chinese population has yet to be validated, including investigation of potential differential item functioning (DIF). To verify the performance of the adapted Chinese CSI, data were collected from 740 participants (235 males and 505 females). Under the item response theory (IRT) framework, the graded response (GR) model was fit. Key assumptions and model fit were checked first, followed by a DIF analysis. Category response curves and information functions were also examined. Results showed that the two IRT assumptions—unidimensionality and local independence—were generally satisfied. The GR model fit the data well. Moreover, the items from the CSI scale performed very well in assessing and differentiating among participants of differing levels of intimate relationship satisfaction. Meanwhile, high test information distributed across a wide range of latent ability ensured that the CSI was reliable and accurate. Moreover, there was no significant DIF for all CSI items, which supported its equity and fairness when administered to different gender groups. Overall, the CSI shows good psychometric characteristics, has no systematic DIF between genders, and holds promise to facilitate further research on intimate relationship satisfaction.