James 1969.

Methods	Randomised double‐blind controlled trial
Participants	Study period: September 1965 to November 1966 (excluding 2 periods during May and August 1966, total of 6 weeks) Setting: children's division of the Los Angeles County‐University of Southern California Medical Center, USA Inclusion criteria: children admitted to hospital with a diagnosis of croup or laryngotracheobronchitis (dyspnoea with inspiratory stridor, subcostal, suprasternal, or sternal retractions, and a barking, seal‐like cough) Exclusion criteria: those with very mild stridor at admission; history of persistent or congenital stridor; suspected diagnosis of acute epiglottitis; clinical or roentgenographic evidence of an associated pneumonitis Baseline demographics (N = 88): proportion male: treatment: 76%; control: 66% median age in months: treatment: 17; control: 12 modified Westley croup score: not reported
Interventions	Treatment (N = 45): single 4 mg/mL dose of intramuscular dexamethasone sodium phosphate Control (N = 43): single 4 mg/mL dose of placebo solution identical in appearance Both the treatment and placebo administered 0 to 3 hours after admission.
Outcomes	Patient improvement at 12 and 24 hours; use of antibiotics and tracheostomy
Notes	Funding source: Merck Sharp & Dohme
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Comment: insufficient information provided to judge.
Allocation concealment (selection bias)	Low risk	Quote: "dexamethasone... and a placebo solution of identical appearance were provided in randomly numbered vials. As each patient was admitted to the study, he received the predetermined dose of medication from the next bottle in the series, after which the bottle was discarded."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "...solution of identical appearance were provided in randomly numbered unlabeled vials" "All of the evaluations were completed before the drug code was broken"
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "...solution of identical appearance were provided in randomly numbered unlabeled vials" "All of the evaluations were completed before the drug code was broken" Comment: outcome measures assessed by staff and in some cases also the investigator. Both staff and investigator appear to have been blinded.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: no missing outcome data
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol identified. All prespecified outcomes from methods appear in 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.