Total Sleep Time (TST) and Columbia jet lag scale scores by study day.

TST was measured using sleep logs (top) and actigraphy (middle). Higher scores on the Columbia Jet Lag Scale (bottom) represent increased feelings of jet lag. Closed circles represent African-Americans and open circles represent European-Americans. N = 20 African-Americans, 17 European-Americans for sleep logs and Columbia jet lag scale. N = 15 African-Americans, 16 European-Americans for Actigraphy. Data are mean ± SEM. Baseline/aligned (days 2–4) and advanced/misaligned (days 6–8) were separated by a phase assessment day (refer to protocol, Fig 1). Asterisks denote significant differences (P ≤ 0.05) between African-Americans and European-Americans as determined by mixed model ANOVAs. There were no significant differences between African-Americans and European-Americans for Columbia Jet lag Scale scores, but there were significant differences for TST.