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Table 5 Percentage changes with 95% CIs in outpatient and inpatient visits for chronic obstructive pulmonary disease (COPD) associated with an interquartile range increases in fine particulate matter (PM2.5) concentration (90.8 μg/m3) on the same day, by different degree of freedom (df) for calendar time, temperature, and relative humidity

From: Short-term effects of ambient fine particulate matter pollution on hospital visits for chronic obstructive pulmonary disease in Beijing, China

  

Outpatient visits

Inpatient visits

Variable

df

Percentage change

95% CI

Percentage change

95% CI

Calendar time

4

1.26

1.11–1.41

5.30

4.47–6.14

 

5

2.38

2.22–2.53

6.03

5.19–6.87

 

6a

2.38

2.22-2.53

6.03

5.19–6.87

 

7

2.38

2.22–2.53

6.03

5.19–6.87

 

8

2.37

2.21–2.52

6.01

5.17–6.86

Temperature

2

2.38

2.22–2.53

6.03

5.19–6.87

 

3a

2.38

2.22-2.53

6.03

5.19–6.87

 

4

2.88

2.72–3.04

6.42

5.57–7.29

 

5

2.66

2.50–2.82

6.52

5.67–7.39

 

6

2.33

2.17–2.49

6.41

5.55–7.27

Relative humidity

2

2.38

2.22–2.53

6.03

5.19–6.87

 

3a

2.38

2.22-2.53

6.03

5.19–6.87

 

4

2.28

2.12–2.44

5.89

5.05–6.74

 

5

2.25

2.09–2.40

5.84

5.00–6.68

 

6

2.25

2.09–2.41

5.87

5.03–6.72

  1. aThe df value used in this study model