Table 8 Multivariate regression model for exhaled breath CO level (ppm): R² (adjusted) = 36.84%, n = 367

Constant

5.20

2.97–7.43

4.59

 < 0.001^*

Duration of cooking (minutes per day)

0.005

0.001–0.010

2.43

0.016*

Civil status

 Single (Reference level)

  Married

0.85

–0.11–1.87

1.74

0.082

  Divorced

3.59

1.17–6.01

2.92

0.004^*

  Widowed

2.02

–0.21–4.25

1.79

0.075

Employability

 Unemployed (Reference level)

  Employed

1.17

0.47–1.86

3.30

0.001^*

Monthly family income (LKR)

 < 14,999 (Reference level)

  15,000–22,499

0.95

–1.17–3.07

0.88

0.378

  22,500–45,999

–0.55

–2.53–1.44

–0.54

0.588

  46,000–149,999

–1.60

–3.63–0.43

–1.55

0.122

  > 150,000

–1.82

–8.42–4.78

–0.54

0.588

Type of the cooking fuel used for the most recent cooking activity^a

 Only firewood only (Reference level)

  Only LPG

–1.98

–2.76– –1.19

–4.96

 < 0.001^*

  Only kerosene

1.89

–1.78–5.57

1.01

0.312

  Firewood plus LPG

–1.62

–2.67– –0.57

–3.04

0.003^*

  Firewood plus kerosene

0.84

–1.45–3.14

0.72

0.471

Having kitchen windows

 Yes (Reference level)

  No

–1.19

–2.50–0.11

–1.80

0.072

Keep the kitchen windows open while cooking

 Yes (Reference level)

  No

0.69

–0.14–1.52

1.62

0.105

Exposure to second-hand tobacco smoking

 Yes (Reference level)

  No

–2.74

–3.53– –1.95

–6.84

 < 0.001^*