Schroder 1989.

Methods	Randomised, parallel‐arm trial Three centres in Germany (community centre clinics) Period of inclusion: March 1986 to February 1988
Participants	Inclusion criteria Age: 17 to 74 years Weight: 55 to 94 kg Exclusion criteria Pregnancy Pretreatment with etretinate or steroids Serious common disease Baseline data: participants were randomised to receive etretinate (n = 15) or placebo (n = 15) Male/female: 12/18 Age (range): 20 to 73 Proportion of participants with psoriatic lesions elsewhere: not specified Withdrawal: not stated
Interventions	Intervention 1 A: etretinate 50 mg once per day (15 participants) Intervention 2 B: placebo (15 participants) Co‐interventions: 2% salicylic ointment Duration of treatment: 4 weeks
Outcomes	No primary or secondary outcome pre‐specified Nb of pustules/4 cm² Percentage of affected area Clinical aspect: 4‐point score
Notes	Funding: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The patients were admitted using a list of randomisation" Comment: no precision on how it was generated
Allocation concealment (selection bias)	Unclear risk	Quote: "either etretin or placebo" Comment: no information on method to guarantee allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "double‐blind study" Comment: however, 65% of participants treated with Tigason had side effects (mainly mucocutaneous side effects), so likely that blinding could have been broken
Blinding of outcome assessment (detection bias) All outcomes	High risk	Quote: "double‐blind study" Comment: however, 65% of participants treated with Tigason had side effects (mainly mucocutaneous side effects), so likely that blinding could have been broken
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: no mention of missing data
Selective reporting (reporting bias)	High risk	Comment: no protocol found to guarantee that all planned outcomes are presented in the results. Not all outcomes cited in the methods were found in the results (clinical aspect: 4‐point‐score)