Figure 3 : Scatter plot showing the relationship between the phase angle of entrainment of the circadian clock to the 24-h day and the free-running circadian period (τ).

From: Circadian rhythms of European and African-Americans after a large delay of sleep as in jet lag and night work

Figure 3

N = 45. Filled circles represent African-Americans (N = 23) and open circles represent European-Americans (N = 22). Phase angle of entrainment was the interval from the phase of the master, internal, circadian clock (assessed by the dim light melatonin onset, DLMO) until dark onset (bedtime = lights out). The DLMO was determined from the phase assessment after the 4 baseline days in the laboratory. A negative DLMO to bedtime interval indicates that the DLMO occurred before bedtime, which is typical. A more negative number on the y-axis indicates a longer time from the DLMO until bedtime. Subjects with shorter free-running periods were entrained to the 24-hour day with earlier circadian rhythms (earlier DLMOs) relative to dark onset (relative to bedtime), and those with longer periods entrained with later circadian rhythms relative to dark. The diagonal line represents a linear fit of the data.