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Table 3 Distribution of the item thresholds and person measures by the SGRQ domain

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

 

Symptoms domain

Activity domain

Impact domain

Range of item threshold

−3.03 – 1.27

−6.42 – 4.46

−1.87 – 2.39

Range of person measure

−4.16 – 3.75

−7.52 – 6.48

−3.72 – 5.11

95 % person measure limitsa

−1.65 – 2.51

−7.47 – 6.48

−1.59 – 5.11

Coverage (%)b

91.67

88.75

72.92

Floor effect (%)

0.83

2.50

0.83

Ceiling effect (%)

7.50

8.75

26.25

  1. aThe 2.5th percentile to 97.5th percentile of person ability
  2. bThe percentage of person measures that fall between the lowest and highest item thresholds