Table 1.

Average sleep duration and variability of 528 youth aged 9–18 y from Mexico City, according to sociodemographic predictors

Sociodemographic predictors	N	Mean sleep duration (min)±SD	Did not meet sleep recommendations,1 %	Mean sleep variability (min)± SD
Sex
Male	252	511 ± 55	41.3	91 ± 43
Female	276	520 ± 60	40.2	95 ± 41
P value2		0.07	0.81	0.36
Age group, years (y)
9.5 to <12 y	93	525 ± 45	65.6	78 ± 37
12 to <14 y	154	522 ± 51	42.9	84 ± 39
14 to <16 y	98	513 ± 55	28.6	99 ± 42
16 to 18 y	183	508 ± 67	32.8	105 ± 44
P value		0.007	<0.0001	<0.0001
Testicular volume (boys only)
<15 mm	41	511 ± 42	58.5	68 ± 31
≥15 mm (latter stages of puberty)	199	511 ± 56	38.2	95 ± 44
P value		0.94	0.02	<0.0001
Menarche status (girls only)
Had not experienced	45	532 ± 49	55.6	81 ± 35
Had experienced	228	519 ± 62	37.3	97 ± 42
P value		0.18	0.02	0.02
Maternal education, years (y)
8 y or less (secondary or primary)	61	520 ± 58	36.1	98 ± 46
9 to 11 y (some high school)	205	519 ± 57	39.5	96 ± 43
12 y (completed high school)	181	516 ± 59	37.6	90 ± 41
>12 y	76	506 ± 58	51.3	88 ± 39
P value		0.15	0.18	0.06
Physical activity, quartiles
Q1, 0 to 5.5 hours/week (h/wk)	136	516 ± 61	39.0	98 ± 47
Q2, 5.8 to 9 h/wk	128	522 ± 58	39.1	94 ± 42
Q3, 9.3 to 14 h/wk	138	510 ± 55	42.0	89 ± 43
Q4, 14.3 to 29 h/wk	126	517 ± 55	42.9	90 ± 36
P value		0.63	0.88	0.10
Screen time, quartiles
Q1, 1 to 22.5 hours/week (h/wk)	135	519 ± 53	42.2	89 ± 41
Q2, 23 to 32.5 h/wk	130	516 ± 58	44.6	94 ± 42
Q3, 33 to 48 h/wk	131	509 ± 59	42.8	93 ± 45
Q4, 48.5 to 116 h/wk	132	520 ± 60	33.3	95 ± 41
P value		0.92	0.25	0.29
Sedentary time in commuting, quartiles
Q1, 3.5 hours/week (h/wk) or less	223	523.7 ± 54.6	36.8	93.7	43.1
Q2, >3.5 h/wk to 5.5 h/wk	57	516.9 ± 58.4	35.1	77.1	35.1
Q3, >5.5 h/wk to 10.5 h/wk	171	511.1 ± 57.1	43.2	98.1	45.0
Q4, >10.5 h/wk to 31.5 h/wk	77	504.7 ± 64.8	50.7	90.7	35.4
P value		0.004	0.12	0.72
Consumed alcohol in the past year
No	61	524 ± 63	37.8	89 ± 37
Yes	342	512 ± 59	38.0	98 ± 43
P value		0.16	0.96	0.14
Ever smoked cigarettes
No	391	518 ± 54	42.4	87 ± 40
Yes	133	509 ± 67	32.3	110 ± 45
P value		0.11	0.02	<0.0001

¹Based on the American Academy of Sleep Medicine recommendations; the recommendation for children <13 years old is between 9 and 12 hours of sleep per 24 hour period, and the recommendation for children 13 to 18 years old is between 8 and 10 hours of sleep per 24 hour period

²P values were obtained from linear regression models with average sleep duration as the outcome and sociodemographic correlate as the exposure. For ordinal characteristics, a P for trend was obtained by including in the model a continuous variable that represented the ordinal categories. For dichotomous characteristics, a Wald test was used.