Table 1 Description of the study population, stratified by educational track

N

191

57

59

75

Age (years)^a

16.8 (16.6–16.9)

16.9 (16.7–17.2)

16.6 (16.4–16.9)

16.8 (16.6–17.0)

 Male^b

49.2 (42.1–56.3)

49.1 (36.3–62.1)

45.8 (33.4–58.7)

52.0 (40.6–63.2)

 Female^b

50.8 (43.7–57.9)

50.9 (38.0–63.7)

54.2 (41.3–66.6)

48.0 (36.8–59.4)

 Once a month or less^b

58.1 (50.9–65.0)

47.4 (34.7–60.4)

55.9 (43.0–68.1)

68.0 (56.5–77.6)

 More than once a month^b

41.9 (35.0–49.1)

52.6 (39.5–65.3)

44.1 (31.9–57.0)

32.0 (22.4–43.5)

 Once a month or less^b

70.2 (63.2–76.3)

59.6 (46.3–71.7)

59.3 (46.3–71.1)

86.7 (76.8–92.7)

 More than once a month^b

29.8 (23.7–36.8)

40.4 (28.3–53.7)

40.7 (28.8–53.7)

13.3 (7.27–23.2)

Social disadvantage^a

1.11 (0.94–1.28)

1.46 (1.11–1.80)

1.00 (0.69–1.31)

0.93 (0.69–1.18)

Self-control^a,c

95.7 (93.8–97.7)

96.7 (93.3–100.1)

89.9 (85.9–92.9)

100.0 (97.0–102.9)

 Cognitive ability (g)^a,c

46.6 (45.6–47.6)

41.3 (39.5–43.0)

46.5 (45.0–48.0)

50.7 (49.6–51.7)

 Reaction time (ms)^a,d

273.0 (268.5–277.5)

283.5 (274.6–292.5)

279.0 (270.6–287.3)

260.3 (255.0–265.6)

 Memory span Forwards^a,c

49.7 (45.8–53.5)

44.3 (37.5–51.1)

50.7 (44.1–57.2)

52.9 (46.5–59.4)

 Memory span Backwards^a,c

37.7 (34.6–40.8)

29.4 (23.5–35.2)

37.0 (32.0–42.0)

44.5 (39–8-49.2)