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Table 2 The model infit index, item difficulty parameters, and separation in the Symptom, Activity, and Impact domain of the SGRQ by the order of item difficulty

From: A psychometric assessment of the St. George’s respiratory questionnaire in patients with COPD using rasch model analysis

Domain/item Infit index Item difficulty (SE) Reliability (separation index)
Symptoms domain    0.59 (1.21)
 S_a5. Very bad unpleasant attacks of chest troubleb 0.85 −1.09 (0.06)  
 S_a4. Attacks of wheezing 0.87 −0.18 (0.06)  
 S_a3. Shortness of breath 0.90 0.09 (0.05)  
 S_a7. How many good days (with little chest trouble) 1.46a 0.23 (0.06)  
 S_a1. Coughed 0.87 0.47 (0.06)  
 S_a2. Brought up phlegm (sputum) 1.08 0.47 (0.06)  
Activity domain    0.86 (2.50)
 A_c1. Sitting or lying still 1.40 −6.42 (0.46)  
 A_c2. Getting washed or dressed 0.93 −3.53 (0.24)  
 A_g1. Take a long time to get washed or dressed 1.08 −3.14 (0.23)  
 A_g2. Cannot take a bath or shower, or take a long time 0.90 −2.84 (0.22)  
 A_c3. Walking around the home 0.86 −2.56 (0.21)  
 A_c4. Walking outside on the level 0.82 −1.39 (0.20)  
 A_g3. I walk more slowly than other people, or I stop for rests 1.09 −0.67 (0.19)  
 A_g4. Jobs such as housework take a long time, or I have to stop for rests 0.81 0.04 (0.19)  
 A_c5. Walking up a flight of stairs 0.92 0.38 (0.20)  
 A_g5. If walk up one flight of stairs, I have to go slowly or stop 0.78 0.61 (0.20)  
 A_c7. Playing sports or games 1.42a 2.54 (0.24)  
 A_g7. Walk up hills, carry things up stairs or play golf 0.80 2.71 (0.24)  
 A_c6. Walking up hills 1.35 2.77 (0.24)  
 A_g6. If hurry or walk fast, I have to stop or slow down 0.86 2.96 (0.25)  
 A_g8. Carry heavy loads, jog or walk at 5 miles per hour or swim 0.69 4.07 (0.30)  
 A_g9. Very heavy manual work, run, cycle, play competitive sports 0.86 4.46 (0.32)  
Impact domain    0.81 (2.08)
 I_h5. Move far from my bed or chair 0.94 −1.87 (0.26)  
 I_f2. I get embarrassed using my medication in public 1.13 −1.30 (0.22)  
 I_f1. My medication does not help me very much 1.25 −1.30 (0.22)  
 I_e5. I do not expect my chest to get any better 0.90 −0.91 (0.20)  
 I_d3. I get breathless when I talk 0.76 −0.72 (0.19)  
 I_d4. I get breathless when I bend over 0.84 −0.62 (0.19)  
 I_h3. Go out of the house to do the shopping 0.88 −0.54 (0.18)  
 I_f3. I have unpleasant side effects from my medication 1.17 −0.54 (0.18)  
 I_f4. My medication interferes with my life a lot 1.07 −0.51 (0.18)  
 I_h4 Do housework 0.87 −0.50 (0.18)  
 I_d1. My cough hurts 0.87 −0.45 (0.18)  
 I_e2. My chest trouble is a nuisance to my family, friends or neighbors 0.99 −0.35 (0.18)  
 I_b2. Chest trouble affect my work 1.21 −0.20 (0.12)  
 I_e3. I get afraid or panic when I cannot get my breath 0.96 −0.17 (0.17)  
 I_i. Best describes how your chest affects youb 0.98 −0.13 (0.10)  
 I_e4. I feel that I am not in control of my chest problem 0.89 −0.11 (0.17)  
 I_h2. Go out for entertainment or recreation 0.80 0.15 (0.16)  
 I_e1. My cough or breathing is embarrassing in public 1.16 0.24 (0.16)  
 I_d2. My cough makes me tired 0.94 0.88 (0.15)  
 I_d5. My cough or breathing disturbs my sleep 1.13 0.93 (0.15)  
 I_h1. Play sports or games 0.88 1.11 (0.15)  
 I_b1. How would you describe your chest condition 2.00a 1.15 (0.08)  
 I_d6. I get exhausted easily 0.90 1.19 (0.15)  
 I_e6. I have become frail or an invalid because of my chest 0.74 1.21 (0.15)  
 I_e8. Everything seems too much of an effort 0.76 1.62 (0.15)  
 I_e7. Exercise is not safe for me 0.89 1.75 (0.16)  
  1. Estimates were obtained from a mixed rating scale and partial credit model by Winsteps
  2. aItem misfit (infit index > 1.4) bReversed item