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Table 4 Nonclustering variables compared across clusters a

From: OMERACT-based fibromyalgia symptom subgroups: an exploratory cluster analysis

Variables Cluster 1b(n = 150) Cluster 2c(n = 171) Cluster 3d(n = 136) Cluster 4e(n = 124) P-valuef
Age, yr 57.0 (14.5) 57.6 (11.3) 52.5 (12.4) 52.2 (9.7) <0.0001
BMI, kg/m2 28.6 (7.6) 31.5 (7.8) 29.2 (6.9) 30.8 (7.8) 0.0030
FM research survey      
WPI 11.1 (3.5) 12.8 (3.7) 12.5 (3.6) 14.3 (3.5) <0.0001
SS 7.6 (1.8) 8.7 (1.8) 9.1 (1.8) 10.5 (1.4) <0.0001
BPI Pain interference 3.4 (1.9) 5.9 (1.8) 5.9 (1.6) 7.9 (1.3) <0.0001
MFI-20      
General 15.0 (2.8) 17.8 (2.1) 17.5 (2.2) 19.0 (1.6) <0.0001
Reduced activity 11.7 (3.9) 15.0 (3.4) 14.6 (3.4) 17.6 (2.3) <0.0001
Reduced motivation 9.8 (3.1) 12.1 (3.5) 12.9 (3.3) 15.5 (2.9) <0.0001
Mental 10.5 (3.8) 12.4 (3.8) 13.9 (3.9) 16.6 (2.9) <0.0001
Total 59.3 (11.8) 74.5 (10.5) 74.4 (10.4) 87.1 (7.1) <0.0001
SF-36      
Physicalg 36.5 (8.3) 26.2 (7.3) 33.1 (6.8) 25.6 (6.4) <0.0001
Mentalg 48.9 (9.3) 45.4 (10.1) 34.5 (9.3) 28.6 (10.3) <0.0001
FIQ      
Tenderness 5.8 (2.8) 7.8 (2.3) 7.7 (2.3) 8.8 (1.6) <0.0001
Impact 5.7 (4.5) 11.5 (5.1) 11.7 (4.7) 16.3 (3.7) <0.0001
Total 34.3 (11.7) 58.1 (13.0) 57.7 (10.8) 77.7 (8.6) <0.0001
POMS      
Anger-Hostility 3.0 (3.3) 3.2 (2.7) 6.8 (4.2) 8.6 (4.4) <0.0001
Vigor-Activityg 6.5 (3.6) 3.9 (3.1) 3.8 (2.8) 2.4 (2.6) <0.0001
Fatigue-Inertia 10.2 (3.7) 13.6 (3.6) 14.7 (3.1) 16.9 (2.6) <0.0001
Confusion-Bewilderment 4.7 (2.9) 6.1 (2.7) 9.1 (2.8) 12.7 (3.2) <0.0001
  1. aData are mean ± SD. BMI, Body mass index; BPI, Brief Pain Inventory; FIQ, Fibromyalgia Impact Questionnaire; FM, Fibromyalgia; MFI, Multidimensional Fatigue Inventory; POMS, Profile of Mood States; SF-36, 36-item Medical Outcomes Study Short Form health survey; SS, Symptom severity; WPI, Widespread pain index. bLow symptom intensity. cModerate symptoms, low negative mood. dModerate symptoms, higher negative mood and dyscognition. eHigh symptom severity. fP-values are from the omnibus analysis of variance test across the four clusters. Pairwise comparisons between clusters also showed significant differences in all cases, except for the following: cluster 1 versus cluster 2 with respect to age (P = 0.62), cluster 1 versus cluster 3 with respect to BMI (P = 0.51), cluster 2 versus cluster 4 with respect to both BMI (P = 0.49) and SF-36 Physical (P = 0.53) and cluster 3 versus cluster 4 with respect to both age (P = 0.86) and BMI (P = 0.08). Differences between clusters 2 and 3 were not significant for all variables, except age, BMI, MFI Reduced Motivation, MFI Mental Fatigue, SF-36 Physical, SF-36 Mental, POMS Fatigue-Inertia and POMS Confusion-Bewilderment. gLower scores are worse for these scales.