Childs 2008

Methods	Design: Randomised cross‐over trial (2 periods) Setting: USA
Participants	N=35, healthy males and females, aged 18‐35 years Participants remained awake throughout overnight sessions between 17.00 and 05.00 Experimental sessions were at least one week apart
Interventions	Caffeine (200mg) containing food supplement Placebo Drugs were identical in appearance Caffeine/placebo capsules were consumed at 03.30
Outcomes	Simple reaction‐time task, two‐choice reaction‐time task performed at 03.00, 04.00 and 05.00
Notes	Funded by a grant from Atlas Labs, USA and by National Institute on Drug Abuse, USA.
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Low risk	Correspondence with author ‐ computer generated randomisation.
Allocation concealment?	Low risk	Central allocation.
Blinding? All outcomes	Low risk	Double‐blind.
Incomplete outcome data addressed? All outcomes	Unclear risk	Insufficient reporting of attrition/exclusions to permit judgement of 'Yes' or 'No'.
Free of selective reporting?	Unclear risk	All outcomes described in Methods section are reported in the Results.
Free of other bias?	Low risk	The study appears to be free of other sources of bias.