Eden 1964.

Study characteristics
Methods	Randomised, double‐blind controlled trial
Participants	Study period: not reported Setting: hospital in the USA Inclusion criteria: children hospitalised for treatment of acute croup, including all children with acute respiratory infections characterised by hoarseness, inspiratory stridor, and a barking cough Exclusion criteria: not reported Baseline characteristics (N = 50): proportion male: not reported age: not reported croup score: not reported
Interventions	All children received as routine therapy oxygen, increased humidity, and tetracycline. Treatment (N = 25): 1 mg/kg intramuscular methyl prednisolone every 6 hours for 24 hours Control (N = 25): 1 mg/kg placebo preparation every 6 hours for 24 hours
Outcomes	Patient improvement at 6, 12, 24 hours
Notes	Funding source: Upjohn Company (supplied drugs for the trial)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The patients were divided into two groups according to a table of random sampling"
Allocation concealment (selection bias)	Unclear risk	Comment: insufficient information provided to permit a judgement
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "The composition of each preparation was unknown to the investigators until the end of the study" Comment: described as double‐blind. Investigators blinded, but it is unclear if participants or personnel (or both) were blinded because who administered the treatments is not stated. Subjective outcomes
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: no description of a third‐party outcome assessor, unclear who performed the measurements. Carried over judgement from blinding of participants and personnel
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: 6% (N = 3) lost to follow‐up due to inadequate evaluation. All losses were in 1 group, but it is unclear which group.
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol identified. All prespecified outcomes in the methods appeared in the results.
Other bias	Low risk	Comment: no other sources of bias identified
Overall risk of bias All outcomes	Unclear risk	Comment: at least 1 domain judged as unclear risk, and no domains judged as high risk