The Patient Reported Inventory of Self-Management of Chronic Conditions (PRISM-CC): testing for bias across patient characteristics and languages

PURPOSE: Developed simultaneously in English and Swedish, the Patient Reported Inventory of Self-Management of Chronic Conditions (PRISM-CC) assesses patients’ perceived difficulty managing life with long-term health conditions. This study assessed the comparability of the PRISM-CC across sociodemographic groups, number of health conditions and language (English and Swedish). METHODS: Differential item functioning (DIF) and differential test functioning (DTF) were analysed by age, gender, education level, and number of conditions using independent English and Swedish datasets. Language-based DIF and DTF were examined using pooled data. An iterative hybrid ordinal logistic regression approach was applied to identify potential DIF across the PRISM-CC’s seven domains. The impact of flagged items on total scores (DTF) was evaluated by comparing test characteristic curves. RESULTS: Few items were flagged for potential DIF in the English, Swedish or pooled data, and only at low cutoff values. The impact of items with potential DIF on DTF was negligible. CONCLUSION: The absence of meaningful DIF and DTF in either the English or Swedish version of the PRISM-CC or between English and Swedish versions provides further support for the PRISM-CC as a valuable tool for assessing self-management ease and difficulty. These results also demonstrate the value of simultaneous development of instruments in two languages. Further evaluation of DIF is necessary in populations with greater self-management challenges, such as among people with severe disease burden.