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Table 1 Baseline characteristics of the Rasch population stratified by disease activity level

From: Psychometric properties of the painDETECT questionnaire in rheumatoid arthritis, psoriatic arthritis and spondyloarthritis: Rasch analysis and test-retest reliability

  low n moderate n high n p-value
RA
 Age (yrs) 60(53.5–65) 100 61(53–68.5) 100 59(50–68.5) 100 0.84
 Duration (yrs) 8(3–17) 93 5.5(2–14) 92 5(1–14) 92 0.03a
 PDQ score 8(5–14) 100 12(7–18) 100 18(12–25) 100 <0.01
 DMARD mono n (%) 65(74) 88 62(75) 83 54(70) 77 0.79
  > 1 DMARD n (%) 23(26) 88 21(25) 83 23(30) 77 0.79
 Biologics n (%) 38(38) 100 33(33) 100 31(31) 100 0.56
 DAS28-crp 2.2(1.8–2.7) 100 3.9 (3.6–4.5) 100 5.7(5.4–6.25) 100 <0.01
 TJC 28 0(0–1) 100 4(3–7.5) 100 13(9–18) 100 <0.01
 SJC 28 0(0–0) 100 1(0–3) 100 5.5(2–9) 100 <0.01
 VAS pain mm 25.5(13–41.5) 100 50(32.5–65) 100 75(57.5–86.5) 100 <0.01
 VAS fatigue mm 29(18.5–56) 100 54(36.5–73.5) 100 77.5(57–92.5) 100 <0.01
 VAS global mm 25.5(13.5–52.5) 100 58.5(41.5–74) 100 82.5(70.5–93.5) 100 <0.01
 HAQ 0.5(0.125–1) 99 1(0.625–1.375) 99 1.75(1–2.25) 100 <0.01
 Crp mg/l 3(1.5–5.5) 100 7(3–14) 100 23.5(11.5–39.5) 100 <0.01
 IgM-RF n (%) 69(80) 86 64(79) 81 58(78) 74 0.96
 Anti-CCP n (%) 31(54) 57 30(51) 59 19(42) 45 0.46
PsA
 Age (yrs) 50.5(42–58) 100 52(41.5–60) 100 52(44–60) 100 0.56
 Duration (yrs) 6(3–9) 91 4.5(1–9.5) 92 6(3–9) 87 0.30
 PDQ score 9(5–12) 100 14(9–18) 100 19(14.5–24) 100 <0.01
 DMARD mono n (%) 69 (95) 73 53(83) 64 54 (81) 67 0.04
  > 1 DMARD n (%) 4(5) 73 11(17) 64 13(19) 67 0.04
 Biologics n (%) 55(55) 100 44(44) 100 41(41) 100 0.11
 DAS28-crp 1.8(1.6–2.35) 92 2.8(2.4–3.55) 92 4.4(3.8–5.1) 90 <0.01
 TJC 28 0(0–1) 94 1(0–3.5) 92 5(2–12) 91 <0.01
 SJC 28 0(0–0) 93 0(0–0) 92 0(0–2) 90 <0.01b
 BASDAI (0–100) 21.5(13–28) 98 52(41–64) 98 77(71–85) 99 <0.01
 BASFI (0–100) 15.5(7–27) 98 45.5(27–57) 98 74(62–86) 99 <0.01
 ASDAS 1.5(1.1–1.8) 97 2.8(2.5–3.1) 97 4(3.7–4.5) 98 <0.01
 VAS pain mm 20.5(12–30) 100 50(39.5–63) 100 77 (68–88.5) 100 <0.01
 VAS fatigue mm 27(15–38) 100 65(48–77) 100 85(75–93) 100 <0.01
 VAS global mm 22(14–30) 100 59.5(46–74) 100 85.5(77–94) 100 <0.01
 HAQ 0.375(0–0.625) 96 0.75(0.51.25) 95 1.5(1–1.875) 96 <0.01
 Crp mg/l 2(1–4) 100 3(1.5–6) 100 6(3–14) 100 <0.01
 HLA-B27 n (%) 7(54) 13 10(53) 19 7(58) 12 0.95
SpA
 Age (yrs) 45.5(36–53) 100 43.5 (35–52.5) 100 47(37–54) 100 0.52
 Duration (yrs) 6(3–13) 94 4.5(2–9) 90 5(2–12) 89 0.14
 PDQ score 8(5–13.5) 100 15(9–19.5) 100 17.5(10.5–22.5) 100 <0.01
 DMARD mono n (%) 24(100) 24 21(84) 25 26(96) 27 0.06
  > 1 DMARD n (%) 0 (0) 24 4(16) 25 1(4) 27 0.06
 Biologics n (%) 78(78) 100 56(56) 100 54(54) 100 <0.01c
 BASDAI (0–100) 22.5(14–34) 100 49(39–61) 100 72.5(65–83) 100 <0.01
 BASFI (0–100) 16(10.5–31.5) 100 40.5(27–56) 100 67.5(49–83.5) 100 <0.01
 ASDAS 1.7(1.3–1.90) 100 2.9(2.5–3.1) 100 4.1(3.8–4.5) 100 <0.01
 VAS pain mm 21.5(12–35) 100 53.5(38–72) 100 75.5(65.5–86) 100 <0.01
 VAS fatigue mm 31.5(17.5–48) 100 65(45.5–81) 100 83(71.5–92) 100 <0.01
 VAS global mm 24.5(15.5–36) 100 61(46–78) 100 84(74–92) 100 <0.01
 Crp mg/l 2(1–4) 100 3(2–7) 100 10(5–21) 100 <0.01
 HLA-B27 n (%) 28(82) 34 20(63) 32 20(67) 30 0.17
  1. Values are the median (interquartile range) or (n (%)). P-values are calculated by Kruskal-Wallis Test, Fishers exact test or Chi square. Except where indicated otherwise there are difference/no difference across all groups according to p value. ano group difference between moderate – high disease activity p = 0.54, bno group difference between low-moderate disease activity p = 0.31, cno group difference between moderate-high disease activity p = 0.78.DMARD Disease Modifying Anti-Rheumatic Drug, DAS28-crp Disease Activity Score 28 –crp, TJC Tender Joint Count, SJC Swollen Joint Count, BASDAI Bath Ankylosing Spondylitis Disease Activity Index, BASFI Bath Ankylosing Spondylitis Functional Index, ASDAS Ankylosing Spondylitis Disease Activity Score, VAS Visual Analogue Scale, HAQ Health Assessment Questionnaire, HLA-B27 Human Leucocyte Antigen-B27, IgM-RF Immunoglobulin M Rheumatoid Factor, Anti-CCP Anti–citrullinated protein antibodies