VALIDATION DATA

Studies have shown the PGA intraclass correlation coefficient (as a measure of test-retest reliability) to be generally acceptable to high, though lower than ones noted for physician global assessment. The data available in the literature do not allow us to directly compare reliability of PGA/global health versus PGA/disease activity; although when tested separately, both appear to have acceptable reliability.

Note: Uhlig et al., ARD 2009 showed the test–retest reliability of patient-reported measures such as DAS28 and its components (including PGA) to be satisfactory when considering the intraclass correlations (ICCs). The ICC for patient global in this study, based on 2 complete assessments within 1 week of 28 stable patients with RA, this was: 0.78.

Link to study:

http://ard.bmj.com/content/68/6/972.full

Smallest detectable difference (SDD): 26.2 mm (Uhlig et al., ARD 2009); 26.2% minimum detectable change (MDC%).

PGA encompasses many aspects of disease which are important for patients and has been shown to have good face validity. Physicians’ assessment of RA disease activity is mainly driven by objective criteria, i.e. tender/swollen joint counts and level of inflammation, whereas it seems patients place more focus on overall well-being, levels of pain and health-related quality of life.

However, the PGA also presents some important challenges, including the patient’s interpretation of the PGA, both depending on the concept (i.e. global health versus disease activity) and on the patient’s individual comprehension of this broad question. The response to the question therefore may both reflect a broad understanding of patient s’ health, and also be influenced by a number of factors, making it difficult to discern what aspect of disease contributes to the overall score. Structural damage (related to disease duration) and other aspects of patients’ lives (such as comorbidities or psychological distress), may have an impact on the scoring of PGA. All these factors need to be taken into account when interpreting individuals’ PGA scores.