Table 1 The item discrimination (a) and difficulty (b) of the modified patient-reported outcome scale for chronic obstructive pulmonary disease (mCOPD-PRO)

1

Did you cough?

1.52

-2.80

-0.36

0.72

2.54

2

Did you have phlegm?

1.30

-2.84

-0.81

0.61

2.75

3

Did you have chest tightness?

1.92

-1.87

-0.75

0.26

2.00

4

Did you have panting?

2.18

-2.20

-0.92

0.05

1.67

5

Did you get short of breath?

2.16

-2.35

-0.86

0.06

1.85

6

Did you feel weak when you talked?

2.18

-1.22

-0.11

0.78

2.07

7

Did you have fatigue?

2.28

-1.74

-0.53

0.27

2.22

8

Did you feel that you were in a poor spirit?

2.07

-1.12

-0.33

1.01

2.33

9

Did you notice cyanosis (your lips, nails, skin, etc. turned purple)?

1.05

-0.54

0.80

2.23

3.43

10

Were you afraid of the wind (cold)?

1.22

-2.04

-0.93

0.37

2.36

11

Did you have abdominal distension?

1.18

-1.00

0.46

1.68

3.65

12

Did you often catch cold?

1.33

-2.74

-0.44

0.71

2.70

13

Were you able to go outdoors alone? (walking, going shopping, having a haircut, taking a bus, etc.)

1.90

-1.21

0.04

1.15

2.37

14.1

Was your cough aggravated by daily activities?

2.13

-1.27

-0.19

0.67

1.98

14.2

Was your chest tightness aggravated by daily activities?

2.69

-1.45

-0.47

0.25

1.55

14.3

Was your panting aggravated by daily activities?

2.43

-1.62

-0.58

0.12

1.50

14.4

Was your shortness of breath aggravated by daily activities?

2.52

-1.56

-0.54

0.19

1.54

15

Did you often feel upset?

2.20

-1.49

0.04

0.96

2.65

16

Did you often feel sad?

2.16

-1.16

0.30

1.46

2.67

17

Did you worry about your illness?

1.98

-1.33

-0.22

0.77

2.03

18.1

Was your cough aggravated by mood swings?

2.71

-0.81

0.23

0.92

2.03

18.2

Was your chest tightness aggravated by mood swings?

2.64

-0.98

0.06

0.82

2.17

18.3

Was your panting aggravated by mood swings?

2.63

-0.91

0.06

0.78

2.75

18.4

Was your shortness of breath aggravated by mood swings?

2.71

-0.87

0.11

0.86

2.73

19

Did the illness affect your contacts with friends, colleagues or neighbors?

2.27

-0.51

0.42

1.22

2.64

20

Was your illness affected by weather changes (cloudy, smoggy, damp, and sultry days, etc.)?

1.24

-3.08

-1.62

-0.40

1.75

21

Did your illness get worse when in a closed or poorly ventilated environment?

1.68

-1.84

-0.79

0.41

2.44