Abdulhamid 2008.

Methods	Double‐blind randomised placebo‐controlled study. Study based in Michigan, USA.
Participants	26 children (aged 7 ‐ 18 years) with CF and mild to moderate lung disease without a concurrent acute severe infection were recruited.
Interventions	Zinc gluconate supplementation (30 mg daily dose) for 12 months vs placebo.
Outcomes	Outcomes not stratified. At each visit, the patient’s interval medical history, height and weight, number of hospitalizations, the use of oral and intravenous antibiotics, pulmonary function test, and physical examination findings were recorded. Primary outcome appears to be number of days of oral antibiotics during active infection per year. Secondary outcomes were production of inflammatory cytokines and IL‐2.
Notes	Dr Abdulhamid has kindly provided a per‐protocol analysis of the data with analysis limited to results of the treatment group compared to that of the placebo group. No specific comment on P. aeruginosa infection.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Described as randomised but method not described.
Allocation concealment (selection bias)	Unclear risk	Concealment of allocation not described
Blinding (performance bias and detection bias) PUFA first	Unclear risk	Both groups (treatment and placebo) were given capsules although these were not described.
Incomplete outcome data (attrition bias) All outcomes	High risk	1 child withdrew (no reason provided) and does not contribute to the data analysis
Selective reporting (reporting bias)	Low risk	In the published study, there is considerable selective reporting with the outcomes reported as per a subgroup analysis comparing those that were previously 'zinc adequate' or 'zinc inadequate'. The thresholds used to define zinc adequacy varied considerably to the 'clinically acceptable normal range'. Dr Abdulhamid has kindly provided the per‐protocol data with groups defined by their treatment group (placebo / zinc supplementation). After the provision of this additional information we therefore judge the risk of selective reporting to be low.
Other bias	Unclear risk	The compliance with treatment is reported as per the subgroup analysis and not as per protocol which further introduces uncertainty.