Chang 2003.

Methods	Study design: randomised controlled trial Total study duration: 10 to 12 days ‐ no long‐term follow‐up beyond end of treatment
Participants	22 patients selected from 130 consecutive referrals who met Rome II criteria for functional constipation and were thought to have 'impaired rectal sensation' defined as rectal sensory threshold volume for desire to defecate of > 90 mL Electrical stimulation: n = 12 (5 male, 7 female) (Age ‐ mean 41 years (range 18 to 71 years) Electromyograph (EMG) biofeedback: n = 10 (6 male 4 female) (Age ‐ mean 53 years (range 28 to 74 years) Duration of symptoms not reported Baseline comparability‐ reported 'no significant difference', but no P values were reported
Interventions	Intervention group: Electrical stimulation using anal plug with pulse generator introduced into the anal canal 'Variant stimulation' parameters scheduled individually within pre‐specified range Performed for 20 minutes daily for 10 to 12 sessions Comparison group: EMG biofeedback with visual changes in pressure activity displayed on monitor 10 to 14 sessions lasting 60 to 90 minutes (frequency not reported)
Outcomes	Symptom questionnaire (bowel frequency and urge, satisfaction with bowel habit, straining, sensation of incomplete evacuation, anal obstruction scored on VAS) Anorectal manometry immediately before and after each treatment Rectal sensation measured using balloon distention
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding (performance bias and detection bias) All outcomes	High risk	Not blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	No attrition
Selective reporting (reporting bias)	Unclear risk	Not registered on a clinical trials registry
Other bias	Unclear risk	Disproportionate number of male participants compared with usual biofeedback population