Table 2

Single model analysis for factors associated with hospital stay at index admission based on DAG

BlockVariableRR 95% CIP value
Demographic characteristicsAge, per 5 years1.02 (1.00 to 1.03)0.032
Male1.04 (0.96 to 1.12)0.312
Lung function and complicationsFEV10.97 (0.95 to 1.00)0.055
Respiratory failure1.05 (0.94 to 1.18)0.396
Pulmonary heart diseases1.03 (0.92 to 1.16)0.624
Hypoxemia0.96 (0.74 to 1.24)0.757
VTE1.38 (1.07 to 1.76)0.012*
Pneumothorax1.63 (0.98 to 2.70)0.057
Hypoxic to hypercarbic encephalopathy1.53 (1.06 to 2.20)0.023*
COPD comorbiditiesCardio/cerebrovascular diseases1.05 (0.98 to 1.13)0.184
Diabetes0.98 (0.90 to 1.07)0.648
Respiratory infection1.12 (1.01 to 1.24)0.035*
Bronchiectasis1.00 (0.88 to 1.13)0.967
Reflux oesophagitis1.00 (0.88 to 1.15)0.959
OSAS1.17 (0.97 to 1.42)0.094
Lung cancer1.09 (0.77 to 1.57)0.62
Anxiety depression0.89 (0.69 to 1.13)0.324
Osteoporosis1.45 (1.07 to 1.96)0.018*
Obesity0.97 (0.86 to 1.08)0.559
Hospital factorsAdmitted on Thursday–Sunday1.04 (0.97 to 1.11)0.319
Admitted from emergency1.08 (1.01 to 1.16)0.033*
Environmental factorsSeason at admission, March–May1.01 (0.91 to 1.12)0.85
Season at admission, June–August1.08 (0.96 to 1.22)0.176
Season at admission, September–November0.98 (0.88 to 1.09)0.752
O3, per 10 ug/m31.00 (0.995 to 1.01)0.573
PM2.5, per 10 ug/m31.00 (0.998 to 1.01)0.217
  • *P<0.05.

  • COPD, chronic obstructive pulmonary disease; DAG, directed acyclic graph; OSAS, obstructive sleep apnoea syndrome; Pre-FEV1, Pre-bronchodilator forced expiratory volume in one second; RR, rate ratio; VTE, venous thromboembolism.