Table 1.
The categorical variables in logistic regression analyses
| Categorical variables | Classification of groups |
|---|---|
| Age group | Nonelderly group (<65 years) |
| Elderly group (≥65 years) | |
| Body mass index (BMI) | Normal (18.5≤ BMI <24 kg/m2) |
| Underweight (BMI <18.5 kg/m2) | |
| Overweight (BMI ≥24 kg/m2) | |
| Education | Elementary school or lower |
| Middle school or higher | |
| Primary fuel for cooking and heating | Biomass fuel including wood, crop |
| residues, dung, and charcoal | |
| Modern fuel such as natural gas, liquefied | |
| petroleum gas, electricity, and solar energy | |
| Ventilated kitchen | None |
| Yes | |
| Smoking intensity | Nonsmoking |
| <5 cigarettes/day | |
| 5–10 cigarettes/day | |
| 11–20 cigarettes/day | |
| >20 cigarettes/day | |
| Smoking duration | Nonsmoking |
| <20 years | |
| 20–39 years | |
| ≥40 years | |
| Second-hand smoking | None |
| Yes | |
| Recurrent respiratory infections | None |
| 1–3 times/year | |
| 4–5 times/year | |
| >5 times/year | |
| Induced cough | None |
| Yes |