Table 1.
Zero-Order Correlations and Descriptive Statistics
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | |
|---|---|---|---|---|---|---|---|---|---|---|
| 1. Sleep duration (hours) | - | |||||||||
| 2. Sleep efficiency (%) | 61*** | - | ||||||||
| 3. Parent-reported sleep problemsa | −.18** | −.05 | - | |||||||
| 4. SES (12 months)b | 24*** | .12+ | −.15* | - | ||||||
| 5. Body mass index (BMI) | −.18** | −18*** | .04 | −.16** | - | |||||
| 6. Percent body fat | −.18*** | −.13* | .03 | −.15** | 84*** | - | ||||
| 7. Waist circumference (WC) | −.14* | −.13* | .04 | −.09 | 89*** | 75*** | - | |||
| 8. SES (8 years)b | 29*** | .15* | −.18** | 82*** | −.19** | −20*** | −.13+ | - | ||
| 9. Sex | .13* | .07 | .04 | −.04 | .02 | 23*** | −.04 | .02 | - | |
| 10. Race/ethnicity | .13+ | .02 | −.01 | .22** | −.04 | −.09 | −.04 | 23*** | .01 | - |
| Mean | 8.11 | 90.33 | 1.76 | .00 | 16.80 | 19.47 | 24.28 | .00 | .50 | .57 |
| Standard Deviation | .71 | 5.44 | .78 | .75 | 2.85 | 6.64 | 2.98 | .80 | - | - |
| Minimum | 5.62 | 67.18 | 1.00 | −1.67 | 13.19 | 5.00 | 16.92 | −2.06 | - | - |
| Maximum | 10.01 | 98.80 | 3.29 | 3.16 | 31.98 | 46.45 | 35.75 | 1.75 | - | - |
| Skewness | −.54 | −1.12 | .61 | −.16 | 1.90 | .92 | 1.39 | −.15 | - | - |
| Kurtosis | .30 | 1.53 | 1.00 | −.45 | 4.84 | 1.36 | 2.39 | −.55 | - | - |
Note.
Sex: 0 = male, 1 = female; Race/ethnicity: 0 = other or multiple races, 1 = non-Latino European American; Sleep duration was actigraphy-measured total number of hours and minutes slept each night on average (excluding wake periods).
Parent-reported sleep problems were reported on using the Child Sleep Habits Questionnaire (Owens et al., 2000), and a mean score was used for each participant rather than a sum score.
SES at 12 months and 8 years were standardized composites of primary caregiver education, secondary caregiver education, and income to needs ratio. Primary caregivers reported on their and their spouse/partner’s level of education with the following categories: (1) less than high school (12 months: 1.0% primary caregiver; .5% spouse/partner); (2) high school or equivalent (12 months: 6.8% primary caregiver; 13.6% spouse/partner); (3) Some college, not graduated (12 months: 22.0% primary caregiver; 19.9% spouse/partner); (4) college degree (e.g., BA, BS; 12 months: 37.2% primary caregiver; 26.7% spouse/partner); (5) Two or more years of graduate school (12 months: 3.7% primary caregiver; 2.1% spouse/partner); (6) graduate or professional degree (12 months: 20.9% primary caregiver; 15.7% spouse/partner). 8.4% of primary caregivers (12 months: 8.9% spouse/partner) declined to provide their highest education level. Income to needs ratios at 12 months: living in poverty (score <1; 9.5% of sample), near the poverty line (score of 1–2; 20.9%), lower middle class (score of 2–3; 23.9%), and middle to upper class (scores >3; 44.8%).
p ≤ .10;
p ≤ .05;
p ≤ .01;
p ≤ .001.