Background
Patient and Public Involvement (PPI) in health research is gaining increased attention and acceptance worldwide. Reliable measurements are crucial to accurately assess, monitor, and evaluate patient involvement efforts in research. The Patient Engagement in Research Scale (PEIRS-22) measures meaningful patient and family caregiver engagement in research. This study focuses on three primary objectives: (1) translation of the PEIRS-22 from English to Danish, followed by linguistic validation and cultural adaptation; (2) assessing the applicability of the Danish PEIRS-22; and (3) focus group interviews to explore the user experiences of PPI.

Methods
A three-phase multi-method study was conducted. In phase one, the PEIRS-22 was translated, linguistically validated and culturally adapted to Danish. In phase two individuals from three distinct patient cancer advisory boards responded to the Danish version of PEIRS-22 to assess its applicability. Three focus group interviews were conducted in phase three, involving individuals from three patient cancer advisory boards.

Results
The translation process resulted in a Danish version of PEIRS-22, conceptually and culturally equivalent to the English version. Overall, among individuals of the three advisory boards (n = 15) the applicability was found to be satisfactory, with no missing data and all items completed. The total PEIRS-22 score among the three advisory boards was 85.2 out of a possible 100, with higher scores indicating greater meaningful involvement. A nested sample of the three patient cancer advisory boards (n = 9) participated in focus group interviews. The analysis yielded four themes: (1) The Danish PEIRS-22 captured the intended cultural meaning and contributed to self-reflection, (2) Internal motivation is a driver for involvement (3), Involvement brought a personal sense of empowerment and (4) Meaningful involvement collaborations are fostered by a trustful atmosphere.

Conclusions
The PEIRS-22 questionnaire has been translated, linguistically validated, and culturally adapted into Danish. We propose that the PEIRS-22 is now ready for use in Danish populations. This study provides a Danish version of the questionnaire that can be used to develop patient-centred practices and foster meaningful involvement and collaborations between patients and researchers in the field of cancer research in Denmark. Personal benefits of participating in PPI can vary, and we recommend using PEIRS-22 in conjunction with a qualitative approach to better explore perspectives on meaningful involvement.