Darbee 1990.

Methods	RCT. Cross‐over design. Each treatment given 2 ‐ 3 times daily for 3 months.
Participants	CF confirmed by sweat test. 13 participants (7 male); mean age 25.7 years, range 18 ‐ 34 years are reported in the abstract. Results from 20 participants were presented at conference. Data on 20 participants was shared with authors. Outcome data for 20 participants were used in the outcome analysis.
Interventions	2 interventions: No washout period between interventions 1. PEP treatment ‐ participants exhaled through a mask for 8 ‐ 10 breaths, then exhaled to a low lung volume through the mask which usually stimulated a cough; this was repeated 5 ‐ 6 times; 2. PDPV ‐ percussion was applied for 3 minutes over all segments, participants breathed deeply several times at each minute, 3 vibrations followed with exhalation through an open mouth, without force, until productive coughing occurred. Participants were instructed to treat until clear, 2 ‐ 3 times per day.
Outcomes	2 measures of mucociliary clearance were repeated after each 3‐month treatment arm: the time taken for half the radiolabeled sputum in the whole lung to clear (T1/2‐W) and the same in the peripheral region (T1/2‐P). Convenience, independence and ease of use was determined with a standardised written questionnaire (not described).
Notes	No statement on withdrawals or dropouts. Participants reported that they got clearer faster with PEP. Published as an abstract only, further information obtained from authors.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Described as randomised, no further details provided.
Allocation concealment (selection bias)	Unclear risk	No information provided.
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Participant and the person providing the therapy were not blinded, no information provided regarding other assessors.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No statement on withdrawals or dropouts. All outcome measure were reported
Selective reporting (reporting bias)	Low risk	All outcome measures were reported in full.
Other bias	High risk	No washout period between each 3 month period of interventions, potential risk for carry‐over effect. Groups similar at baseline regarding the most important prognostic indicators.