European Scleroderma Study Group to define disease activity criteria for systemic sclerosis. III. Assessment of the construct validity of the preliminary activity criteria

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Abstract
Objective: To further assess the construct validity of the three European Scleroderma Study Group (EScSG) preliminary activity indices for systemic sclerosis (SSc): for SSc as a whole, for diffuse SSc (dcSSc), and for limited SSc (lcSSc). Methods: 30/290 SSc clinical charts collected for the EScSG study used to develop activity criteria for SSc were selected and sent to four clinical experts in SSc. The experts ranked the charts from 1 to 30 (1=lowest activity, 30=highest activity). The relationships among the ranks given by each investigator and each of the three scores, and between any two of the ranks were investigated. Results: A consistently significant correlation (rs=0.530–0.712) was found between the ranks given by each of the four investigators and the index for the entire patient group. A similar level of agreement was detected between each couple of the four experts (rs=0.428–0.720). Moreover, the ranks given in patients with an index >3 were significantly higher than those given for patients with an index ⩽3. This cut off point had previously been shown to best discriminate patients with active disease. Conclusions: Of the originally developed activity indexes, the whole series index has been externally validated. The index comprises the first preliminary, but necessary, groundwork to improve the concept of disease activity in SSc, which is still ill defined. It can be used as a preliminary activity index in clinical investigational studies.