Boxplots of the step 2 scoring results displaying differences in diagnostic confidence between correct and incorrect diagnoses. CT: computed tomography; DC: diagnostic confidence; κ: Fleiss kappa; MRI: magnetic resonance imaging; n_c: number of correct diagnoses; n_ic: number of incorrect diagnoses; RG: reader group (based on their years of experience in musculoskeletal imaging); RG1: inexperienced reader group; RG2: semi-experienced reader group; RG3: experienced reader group; XR: X-ray. The symbols (ns: P > 0.05, *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, ****P ≤ 0.0001) represent the results of the conducted Mann–Whitney U test. Except for RG1 in XR, self-reported DC scores were significantly different between correct and incorrect axSpA diagnoses. In addition, the figure also shows that RG3 tended to be more confident in their diagnoses than the two less experienced RGs