Table 3 Chronic respiratory questions asked in a study of male coal miners comparing numbers and percentage of the affected among development, mine and other production workers stratified by smoking habit

Do you usually cough first thing in the morning?

Never smoker

8(20.5%)

14(25.9%)

20(21.1%)

42(22.3%)

0.754

All

10(21.3%)

21(26.9%)

29(23.2%)

60(24.0%)

0.741

Do you usually cough during the day or at night?

Never smoker

11(28.2%)

14(25.9%)

19(20.0%)

44(23.4%)

0.520

All

13(27.7%)

21(26.9%)

28(22.4%)

63(25.2%)

0.593

If the response was yes to any of the above, the worker was asked:

Do you usually cough as much as 4–6 times a day for 4 or more days in a week? (Yes/no)

Never smoker

8(20.5%)

6(11.1%)

4(4.2%)

18(9.6%)

0.013

All

11(23.4%)

10(12.8%)

7(5.6%)

14(5.6%)

0.004

Have you coughed like this on most of days for as much as 3 consecutive months or more in a year? (Yes/no)

Never smoker

4(10.3%)

2(3.7%)

3(3.2%)

9(4.8%)

0.197

All

5(10.6%)

5(6.4%)

4(3.2%)

14(5.6%)

0.156

For cough with sputum production, a worker was asked:

Do you usually cough with sputum first thing in the morning? (Yes/no)

Never smoker

7(17.9%)

10(18.5%)

12(12.8%)

29(15.5%)

0.580

All

9(19.1%)

15(19.2%)

18(14.3%)

42(16.9%)

0.614

Do you usually cough with sputum during the day or at night? (Yes/no)

Never smoker

7(17.9%)

8(14.8%)

8(8.4%)

23(12.2%)

0.246

All

9(19.1%)

12(15.4%)

12(9.6%)

33(13.2%)

0.203

If the response was yes to any of the above:

Do you usually cough with sputum as much as 4–6 times a day, or 4 or more days in a week? (Yes/no)

Never smoker

4(10.5%)

3(5.6%)

2(2.1%)

9(4.8%)

0.117

All

4(8.7%)

6(7.7%)

5(4.0%)

15(6.0%)

0.393

Have you coughed with sputum on most of days for as much as 3 consecutive months or more in a year? (Yes/no)

Never smoker

3(7.7%)

1(1.9%)

0

4(2.1%)

0.019

All

3(6.4%)

2(2.6%)

3(2.4%)

8(3.2%)

0.387

Workers were classified as having breathlessness if they answered yes to:

Are you troubled by shortness of breath when hurrying on level ground? (Yes/no)

Never smoker

17(43.6%)

17(31.5%)

33(34.7%)

67(35.6%)

0.469

All

21(44.7%)

25(32.1%)

40(32.0%)

86(34.4%)

0.258

Do you get shortness of breath walking with other people of your own age on level ground? (Yes/no)

Never smoker

7(17.9%)

2(3.7%)

3(3.2%)

12(6.4%)

0.004

All

8(17.0%)

5(6.4%)

3(2.4%)

16(6.4%)

0.002

If the response was yes to any of the above:

Do you have to stop for breathing when walking at your own pace on level ground? (Yes/no)

Never smoker

2(5.1%)

1(1.9%)

3(3.2)

6(3.2%)

0.675

All

3(6.4%)

4(5.1%)

4(3.2%)

11(4.4%)

0.617

Have you experienced wheezing sound from your chest? (Yes/no)

Never smoker

5(12.8%)

4(7.4%)

5(5.4%)

14(7.5%)

0.335

All

6(12.8%)

6(7.7%)

8(6.5%)

20(8.1%)

0.403