Table 1.

Study sample characteristics for wave 1 of the sleep study, Chicago site of CARDIA, 2003-2004.

N	647
Mean (standard deviation)
Mean age in years	42.9 (3.6)
Mean objective sleep duration in hours	6.06 (1.16)
Mean subjective sleep duration in hours	6.83 (1.11)
Proportion
Female	0.58
Black	0.44
College graduate	0.51
Income ≥ $35,000/year	0.67
Obese	0.33
High depression score	0.17
Fair or poor self-rated health	0.07
Low sleep efficiency	0.32
High risk of apnea	0.14
High sleepiness	0.23
High sleep variability	0.37