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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