Wakefield 2002.

Methods	Country: Australia Setting: recruited from paediatric outpatient clinics, intervention by mail and phone CT: alternation by week of attendance at clinic
Participants	292 smoking parents of children aged 1 to 11 with asthma
Interventions	At baseline, urine analysed for cotinine:creatinine ratio Intervention: parents sent a letter signed by the study co‐ordinator to explain child's baseline cotinine:creatinine ratio, and to encourage banning smoking at home. Two booklets enclosed: 1 explained the effects of ETS on children and gave advice to parents on its restriction; the other concerned quitting. The index parent was contacted by telephone 1 week and 1 month later for advice and encouragement. Control: usual advice about smoking from doctors and nurses
Outcomes	At 6 months: • Smoking bans at home Secondary study outcomes: • Parent reports of bans on smoking in car • CPD • Child urinary cotinine • Parent‐reported cessation
Type of intervention	Child with health problems (ill‐child health care)
Notes	Retention 264/292 (90.4%)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	"Families were allocated by alternate week to either an intervention or control group."
Allocation concealment (selection bias)	High risk	No information was provided, but method of sequence generation makes allocation concealment highly unlikely.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Similar rates lost to follow‐up in both groups (10.5% intervention, 8.7% control)
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Children's cotinine levels used to validate self‐report of smoking bans