Figure 2. Classification tree for RA development or treatment intensification in ACPA-negative undifferentiated arthritis. Classification tree analysis was used to explore the hierarchical structure of baseline predictors of the composite outcome of RA development or treatment intensification among patients with available follow-up data. The first split was based on the presence of large-joint involvement. Among patients with large-joint arthritis, concomitant hand involvement further enriched the probability of outcome occurrence. Among patients without large-joint involvement, CRP elevation identified a higher-risk subgroup. The terminal split based on swollen wrist involvement should be considered exploratory and less robust than the preceding branches. Red boxes indicate patients who developed RA or required treatment intensification; green boxes indicate patients who remained stable. Percentages within each node refer to the proportion of patients with or without the composite outcome within that node, while total percentages refer to the proportion of the whole analysed population. ACPA, anticitrullinated protein antibodies; CRP, C reactive protein; RA, rheumatoid arthritis.
