Smith 2013.

Methods	RCT (parallel design) Study duration: 12 months Setting: 29 general practices in south east of England, UK
Participants	3968 eligible, 146 randomly assigned, 120 completed the study Intervention (expressive writing): 55 Control (writing on time management): 65 Age: mean 36 (SD 6.99) years Sex: male 34, female 112 Physician‐diagnosed asthma Inclusion criteria: adults (18 to 45 years old) with a diagnosis of asthma and requiring regular inhaled medication (British Thoracic Society step two and above) Exclusion criteria: receipt of psychotherapy, diagnosis of psychotic disorder in the past, unable to understand English, having work or travel commitments during the trial period
Interventions	Intervention: write about very deepest thoughts and feelings about a stressful experience. Participants could write about the same topic for three sessions or move from one topic to another Control: write on a factual account of activity over the day (day 1), food and drink consumed (day 2) and leisure time activity (day 3) Participants in both groups wrote in their own home for 20 minutes daily for three consecutive days.
Outcomes	FEV1 % predicted and FVC (absolute values) using spirometer (vitalograph), quality of life (Mark’s Asthma Quality of Life Questionnaire), asthma symptoms (Symptom Score Questionnaire), distress caused by asthma (Asthma Bother Profile), medication use (corticosteroid and beta agonist use measured as puffs per day) and asthma‐related healthcare utilisation (measured as asthma‐related GP or hospital visits) Outcomes measured at baseline and at 1, 3, 6 and 12 months post intervention
Notes	Abstract only, full results extracted from draft manuscript (unpublished) Sample size calculation reported Intervention and control groups similar in terms of demographic characteristics, smoking history and asthma‐related outcome measures Study funded by Asthma UK
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Participants were allocated to one of the two study groups, using computer generated randomised blocks of 12, changing to blocks of six as recruitment slowed"
Allocation concealment (selection bias)	Low risk	Study author confirmed the use of sealed opaque envelopes for assignment
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"The writing tasks were supplied in sealed envelopes to ensure researcher blinding. Participants were informed that the trial was examining the effect of two writing tasks to ensure that participants remained blinded"
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Study author confirmed the blinding of outcome assessors
Incomplete outcome data (attrition bias) All outcomes	Low risk	Dropout balanced in numbers across the two groups (13 in intervention and 11 in control) with similar reasons for missing data
Selective reporting (reporting bias)	Low risk	All possible outcomes stated in the methods section reported in the results section
Other bias	Low risk	No evidence of further systematic bias