Signalling questions	Description	Response options
2.1. Were participants aware of their assigned intervention during the trial?	None (participants) indicated that they guessed the actual study aims Study coordinators guessed that 52%, 51%, 41% and 44% of participants who received caffeine described as caffeine, caffeine described as placebo, placebo described as placebo and placebo described as caffeine, respectively, received caffeine, indicating the success of blinding	PN
2.2. Were carers and people delivering the interventions aware of participants' assigned intervention during the trial?		PN
2.3. If Y/PY/NI to 2.1 or 2.2: Were there deviations from the intended intervention that arose because of the experimental context?		NA
2.4. If Y/PY to 2.3: Were these deviations from intended intervention balanced between groups?		NA
2.5 If N/PN/NI to 2.4: Were these deviations likely to have affected the outcome?		NA
2.6 Was an appropriate analysis used to estimate the effect of assignment to intervention?		PY
2.7 If N/PN/NI to 2.6: Was there potential for a substantial impact (on the result) of the failure to analyse participants in the group to which they were randomized?		NA
Risk‐of‐bias judgement		Low

Note: N, No; NI, No Information; PN, Probably No; PY, Probably Yes; Y, Yes.