Both studies that provided **data** to this research have been conducted in compliance with the ethical principles for medical research involving human subjects, as defined in the Declaration of Helsinki and the European General Data Protection Regulation. For the Dutch DeepSpA study, the local Medical Ethical Committee (METC MUMC/UM) approved the study (MEC 15-4-100). For the English SPeAk study, the study has been approved by the Edinburgh Medical School Research Ethics Committee (REC reference 20-EMREC-007). All participants provided informed consent before completing any study-related procedures; participants had to have capacity to consent to participate in this study. For both studies, each participant gave written informed consent before the assessment.