Foged 1983.

Methods	Double‐blind, randomised, parallel‐arm trial Multi‐centre Period of inclusion: winter 1980 to 1981
Participants	Inclusion criteria Not stated Exclusion criteria Pregnancy Methotrexate or PUVA therapy in the last 4 weeks Baseline data: randomised to etretinate 1 mg/kg once daily (n = 24) or placebo (n = 26) Median age (range), years: 55 (26 to 78) Male/female: 8/42 Median duration of condition (range), years: 3 (0 to 30) Proportion of participants with psoriatic lesions elsewhere: not specified Withdrawal: etretinate (n = 4); placebo (n = 5) Adverse events: 2; 0 Reasons unrelated to treatment: 3 Lack of effect: 0; 4
Interventions	Intervention A: etretinate 1 mg/kg once daily (24 participants) Control intervention B: placebo (26 participants) Co‐interventions: none Duration of treatment: 8 weeks
Outcomes	No primary or secondary outcome pre‐specified Response using an ordinal scale Adverse events
Notes	Funding: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "After informed consent, 24 patients were allocated to 8 weeks of oral etretinate treatment and 26 patients to placebo" Comment: insufficient information about the sequence generation process to permit judgement
Allocation concealment (selection bias)	Unclear risk	Comment: unclear because the method of concealment is not described
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "double‐blind" Comment: likely that blinding could have been broken because of etretinate's side effects, mainly symptoms from skin and/or nasobuccal mucous membranes
Blinding of outcome assessment (detection bias) All outcomes	High risk	Quote: "double‐blind" Comment: likely that blinding could have been broken because of etretinate's side effects, mainly symptoms from skin and/or nasobuccal mucous membranes
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: "9 patients withdrawn during trial were used in analyses of side effects only: etretinate (4); placebo (5) Adverse events: 3; 0 Did not fulfil selection criteria: 1; 0 Transfered to operation: 0; 1 Inefficacy: 0; 4" Comment: 20% of missing data with unbalanced reason by group; not specified how study authors dealt with it
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol found to guarantee that all planned outcomes are presented in the results