Cluster analysis results projected on a biplot. BDI = Beck Depression Inventory; BPIAVP = Brief Pain Inventory - average pain intensity; BPIPIF = Brief Pain Inventory - pain interference score; CGIS = Clinician Global Impression of Severity; FIQPI = Fibromyalgia Impact Questionnaire physical impairment; FIQx = Fibromyalgia Impact Questionnaire item x; PGII = Patient Global Impression of Improvement; SF36M = 36-item short form questionnaire – mental composite summary score; SF36P = 36-item short form questionnaire – physical composite summary score; SDSx = Sheehan Disability Scale domain x. Note: Symbols indicate patients, rays indicate outcome variables. Angles between rays reflect the degree of association between variables: variables that are highly related would be shown as co-directional rays (if positively correlated) or anti-directional (if negatively correlated); coordinates for patients are based on the first 2 principal components and, for the outcomes, on the loadings of individual variables on the principal components. Patients with similar outcomes are grouped together in the multivariate space which agrees with the class memberships from cluster analysis, indicated by color and symbol. Numbers in boxes indicate the centers of the respective cluster. The point at the intersection of the axes is associated with a hypothetical patient having average scores for all outcomes.