Harackiewicz 1988.

Methods	Setting: university campus health centre/medical centre, USA Recruitment: smokers applying for free cessation programme
Participants	98 smokers in relevant arms, 61% female, average age 35, average cpd 27 for all participants
Interventions	All received advice from a doctor or nurse to quit by using the written materials, which were different for each group ∙ Self‐help manual employing intrinsic motivation approach (Stopping Smoking on Your Own with Nicorette) and nicotine gum ∙ Self‐help manual employing extrinsic motivation approach (The Doctor's Program for Stopping Smoking with Nicorette) and nicotine gum ∙ Intrinsic motivation self‐help manual only ∙ Control ‐ short booklet only, with no motivational element
Outcomes	Sustained abstinence at 12 months (3 months to 12 months) Validation CO < 8 ppm at each visit; saliva thiocyanate < 10 mg/dL at 3 months and 6 months; 2 participants reclassified as smokers
Notes	3 vs 4 for self‐help compared to control 1 and 2 not used
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"Randomly assigned"; method not described
Allocation concealment (selection bias)	Unclear risk	No details given
Blinding (performance bias and detection bias) All outcomes	Low risk	Biochemical validation; groups differed in intervention contact but not in intensity
Incomplete outcome data (attrition bias) All outcomes	Low risk	22 of 197 participants did not attend any follow‐up and were excluded from analyses "drop‐out rates did not differ according to condition" Other losses assumed to be smoking