Howard 2010.

Methods	Trial design: Randomised cross‐over trial Intervention setting: Sleep disorders research unit Shift system: At least one night shift per fortnight during the six months preceding the study (21:00‐07:00) Follow‐up period (intervention plus follow‐up): 1 night (Washout period): Minimum of 2 weeks
Participants	Inclusion criteria: None reported Exclusion criteria: Visual impairment that did not correct with eye‐glasses; regularly used sedative medications; history of sleep apnoea or clinical features of sleep apnoea; chronic sleepiness (score greater than 10 on the Epworth Sleepiness Scale) Number screened: Not reported Number eligible: Not reported Number included in our analysis: n = 8 Industry: Sleep research Age in years: (mean ± SD): 31 ± 9.6 Gender: 75% female Country: Australia "Chronotype" or morningness/eveningness score: Not reported
Interventions	Intervention: Exposure to a nap Shift‐based timing: Night (on‐shift) Hours of intervention: 04:00 Dose/frequency/duration: 30 minutes per exposure,1 exposure per night for 1 night Control/comparison intervention: No‐nap participants were requested not to sleep after 12:00 noon on each day of testing, and have a minimum of 7 hours sleep on the night prior to the session additional control group: nap in the evening, prior to the night shift (not analysed for this review)
Outcomes	Outcomes (measurement tool and timing), relevant to current review: Sleep length off‐shift: Outcome not examined Sleep quality off‐shift: Outcome not examined Sleepiness on‐shift: subjective: Karolinska Sleepiness Scale (at baseline visit: 20:15 plus four times during shift: 20:15, 03:45, 04:30, 06:45) objective: Psychomotor Vigilance Task (at baseline visit: 20:15 plus four times during shift: 20:15, 03:45, 04:30, 06:45)
Notes	Funding: VicRoads
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"alternating sequence"
Allocation concealment (selection bias)	Unclear risk	No information
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Participants were not advised in advance which condition they would be participating in on a given night (of 3 possibilities)
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No information (see Applicability of design)
Incomplete outcome data (attrition bias) All outcomes	Low risk	Participants completed all experimental conditions
Selective reporting (reporting bias)	Low risk	All expected outcomes reported
Outcome reliably or objectively measured	Low risk	Karolinska Sleepiness Scale; Psychomotor Vigilance Task Test
Other potential sources of bias	Unclear risk	We deem a 2‐week washout period sufficient to avoid a possible carry‐over effect. However, no main effect testing was reported for period effect Notable: "...sleep inertia...may have played a role in the lack of significant performance improvement following the morning nap in the current study"