Table 1 Descriptive statistics for control and independent model variables

Sex

Male

53.3 %

.13

Female

46.7 %

(.12)

Education

University preparatory

8.9 %

-.19

Senior general

22.0 %

(.12)

Junior general

34.2 %

Preparatory vocational

34.8 %

Ethnicity

Not Dutch

4 %

-.47

Dutch

96 %

(.12)

Age of smoking initiation

11.67 (1.90)

Baseline smoking

<1 per day

83.7 %

2.70

1-5 per day

9.6 %

(.21)

6-10 per day

5.2 %

>10 per day

1.4 %

DRD2 Taq1A

A2A2

64.2 %

.59

A2A1/A1A1

35.8 %

(.12)

DRD4 48 bp

<7-repeat

64.2 %

.60

VNTR

≥7-repeat

35.8 %

(.12)

OPRM1 A118G

AA

78.7 %

1.41

AG/GG

21.3 %

(.12)

Parental smoke exposure

No smoking parents

54.0 %

1.00

Smoking parent(s)/no exposure

10.2 %

(.13)

One smoking parent/exposed

22.5 %

Two smoking parents/exposed by one

2.3 %

Two smoking parents/exposed by both

11.0 %