Table 1 Sociodemographic characteristics of the study participants for the total population and by different outcomes

Potential confounders

%

n

%

n

%

Sex

 Female

46

28

22

44

35

 Male

54

38

26

49

33

Age

 6–7 years

27

14

19

25

34

 8–9 years

31

24

28

25

29

 10–11 year

30

17

21

31

38

  ≥ 12 years

12

11

33

12

36

Living with both parents (NA = 9)

 No

29

28

35

29

36

 Yes

67

38

21

62

34

Parental atopic disease (NA = 30)

 No

58

27

17

43

27

 Yes

31

32

38

43

51

Mother working (NA = 14)

 No

69

54

27

63

33

 Yes

25

11

16

26

38

Father working (NA = 22)

 No

8

7

32

6

27

 Yes

84

51

22

81

35

Hours child stay at home (NA = 61)

  < 3 h

7

5

25

5

25

 3-6 h

17

11

24

18

39

  > 6 h

54

44

30

58

39

Place child most of the time (NA = 9)

 Inside

38

22

21

33

31

 Outside

59

43

27

58

36

Smoking in child’s presence (NA = 28)

 No

65

44

24

63

35

 Yes

24

19

28

24

36

Paved street near to house (NA = 10)

 No

21

18

32

19

33

 Yes

76

48

23

74

36

Type of heater (NA = 69)

 Other

29

21

26

29

36

 Coal and gas

46

34

27

41

33

Gold mine distance

 1st quartile

25

22

32

28

41

 2nd quartile

25

12

17

20

29

 3rd quartile

26

20

28

22

31

 4th quartile

24

12

18

23

35

Copper mine distance

 1st quartile

25

21

30

31

45

 2nd quartile

25

14

20

21

30

 3rd quartile

25

14

20

20

29

 4th quartile

25

17

25

21

31

Average distance to both mines

 1st quartile

25

24

34

31

44

 2nd quartile

25

11

16

21

31

 3rd quartile

25

15

22

19

28

 4th quartile

25

16

24

22

32