Translation, cross-cultural adaption, validity and reliability of a composite physical function scale for adults aged 65 + years in a Danish context

BACKGROUND: To prevent or postpone dependence on help in everyday activities, early identification of adults aged 65 + years at risk of functional decline or with progressing functional decline is essential. The American Composite Physical Function (CPF) scale was developed to detect and prevent this age-conditioned decline. In this study, the aim was to translate and adapt the scale into a Danish version and assess the validity and reliability in Danish adults aged 65 + years. METHODS: A forward–backward translation procedure was used, followed by an expert panel review to finalise the Danish version of the CPF scale. In the subsequent pre-test, three-step cognitive interviews and hypotheses testing were performed to evaluate the validity, and a test–retest was done to assess reliability. RESULTS: In the pre-test, 47 adults participated in three-step cognitive interviews, and 45 adults answered an online version of the scale. In terms of content validity, the scale was relevant and easy to answer, although many informants skipped the instruction to the questionnaire, which may negatively impact face validity. Construct validity showed a significant difference in CPF scores in adults aged 65 + years by residence and activity level and a decreasing CPF score with increasing age. The reliability test showed an excellent kappa (0.92). CONCLUSION: The scale covering daily activities helps to identify adults aged 65 + years with reduced physical functions or at risk of loss of independence. Further research is needed to assess the CPF predictive value for adults aged 65 + years at risk of or with a progressing physical decline. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12877-023-04240-2.