Williams 1988.

Methods	Country: USA. Study sites: not stated Study period: not stated. Recruitment: via the newsletters of three manufacturers in Northeastern Pennsylvania, USA. Sample size calculation: not mentioned.
Participants	Number of participants: 60 smokers (20 in each group). Inclusion criteria: smokers who had attended at least one other smoking cessation programme, and who worked for one of 3 companies. Exclusion criteria: not stated. Overall demographics: 31 male (51.7%), ages 21 to 58, smoked an average of 36.4 CPD over an average of 5.32 years and had attended at least one other smoking cessation programme.
Interventions	a) Hypnosis ‐ single 2.5‐hour group session using an adaptation of Spiegel (1970) and Stanton (1978) procedure. There were two 45‐min hypnosis trials, followed by a 45 min question period to help subjects understand procedure, alleviate misconceptions and clarify self‐monitoring procedure + post‐hypnotic suggestion to take away b) Placebo control ‐ single 2.5‐hour group discussion of reasons for smoking and attempts to quit. c) No treatment control ‐ received instructions on self monitoring and 12‐month waiting list. Duration of intervention: 2.5 hours. Duration of follow‐up: 48 weeks (12 months).
Outcomes	Definition of smoking cessation: point prevalence abstinence at 48 weeks Adverse events: no information provided on whether or not AE data were collected and whether any AEs occurred.
Notes	Funding: participants were told that their companies were sponsoring the programme in the interest of employees' health Author declaration of interest: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomized, method not stated
Allocation concealment (selection bias)	Unclear risk	No details given
Blinding of outcome assessment (detection bias) All outcomes	High risk	Blinding not possible due to nature of intervention, self‐report only
Incomplete outcome data (attrition bias) All outcomes	Low risk	No missing outcome data
Selective reporting (reporting bias)	Low risk	All outcomes reported as described in the methods section
Other bias	High risk	Waiting list control; control group aware they would later receive intervention which may have discouraged quitting in this arm.

AE: adverse events
 CO: carbon monoxide
 CPD: cigarettes per day
 FTND: Fagerstrom Test for Nicotine Dependence
 ITT: intention to tream
 LTFU: lost to follow‐up
 NRT: nicotine replacement therapy
 ppm: parts per million
 PTSD: post‐traumatic stress disorder
 RCT: randomized controlled trial
 TQD: target quit date