Ellis 1982 (chole).

Study characteristics
Methods	Parallel, 5 days
Participants	PCA 15, control 17 (third group receiving sublingual buprenorphine not reported here) Cholecystectomy
Interventions	PCA: meperidine. Bolus/lockout/4 h limit: NR Control: IM morphine 10 mg prn according to usual practice of nursing staff
Outcomes	Pain intensity, opioid consumption, pulmonary function tests, sedation, nausea, patient satisfaction and preference
Source of funding	Not reported
Notes	QS = 2 (R = 1, DB = 0, W = 1)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not explicitly stated, but appears to be unblinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	Appears that all participants completed the study (although not explicitly stated)
Selective reporting (reporting bias)	Low risk	All outcomes described in Methods section are reported in Results section.
Other bias	High risk	Very small sample size