Table 1.

Sleep Duration, Sleepiness, and Alertness among Interns, According to Shift Type and Duty-Hour Group.^*

Shift Type	Mean Hours of Sleep (95% CI)	Mean Score on Karolinska Sleepiness Scale (95% CI)†	Mean No. of Performance Lapses on PVT-B (95% CI)‡
Flexible programs
Day shift	6.89 (6.61–7.16)	4.5 (4.2–4.7)	4.9 (3.3–6.4)
Day 1 of extended overnight shift	7.67 (7.39–7.95)	4.3 (4.0–4.5)	4.7 (3.1–6.2)
Day 2 of extended overnight shift	5.12 (4.84–5.40)	6.8 (6.5–7.0)	7.8 (6.3–9.4)
Day off	9.05 (8.77–9.33)	4.2 (3.9–4.4)	3.9 (2.4–5.5)
Other§	6.11 (5.79–6.43)	4.8 (4.2–5.4)	6.6 (4.6–8.6)
Across shifts	6.85 (6.61–7.10)	4.8 (4.7–5.0)	5.3 (3.7–7.0)
Standard programs
Day shift	6.74 (6.46–7.02)	4.7 (4.5–5.0)	5.8 (4.2–7.3)
Night shift	7.35 (6.87–7.83)	4.9 (4.5–5.3)	5.6 (3.9–7.3)
Day off	8.81 (8.52–9.10)	4.0 (3.8–4.3)	4.4 (2.9–5.9)
Other§	6.78 (6.45–7.11)	4.9 (4.6–5.3)	6.3 (4.6–7.9)
Across shifts	7.03 (6.78–7.27)	4.7 (4.6–4.9)	5.7 (4.1–7.3)

^*Confidence intervals have not been adjusted for multiple comparisons, and inferences drawn from the intervals may not be reproducible.

^†Scores range from 1 (extremely alert) to 9 (extremely sleepy, fighting sleep).

^‡Performance lapses on the brief Psychomotor Vigilance Test (PVT-B) were defined as reaction times of more than 355 msec. A higher number of lapses indicates lower levels of alertness.

^§In flexible programs, days that had missing shift information or were classified by the interns as having a regular night shift were reclassified as “other” (see Section 8 in the Supplementary Appendix). In standard programs, days that had missing shift information or were classified by the interns as starting or finishing an extended overnight shift were reclassified as “other.”