Warwick 1990.

Study characteristics
Methods	RCT. Cross‐over design. Location: single centre in USA. Duration: not clear.
Participants	Reported 13 pairs of samples but number of participants was not specified, therefore we can only assume there were 13 adolescents or adults. Age and sex not specified.
Interventions	HFCWO versus CPT. Participants were randomised to 2 groups each with 4 sessions. 1st group: CPT, HFCWO, HFCWO, CPT. 2nd group: HFCWO, CPT, CPT, HFCWO.
Outcomes	Wet and dry sputum weight.
Notes	Interventions looks like 2 sessions just one the reverse of the other.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Described as randomised but method not discussed.
Allocation concealment (selection bias)	Unclear risk	Not discussed.
Blinding (performance bias and detection bias) All outcomes	High risk	Not possible to blind participants or clinicians.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Reported 13 pairs of samples but number of participants was not specified, therefore we can only assume there were 13 adolescents or adults.
Selective reporting (reporting bias)	Unclear risk	Abstract only.
Other bias	Unclear risk	Age and sex of participants not stated.