Lindelof 1990.

Methods	Within‐patient, randomised trial One centre in Stockholm Period of inclusion not stated
Participants	Inclusion criteria Not stated Exclusion criteria Therapy during the 3 weeks preceding the trial Baseline data: active treatment of lesions on 1 side of the body vs control on the other side (17 participants) Median age (range), years: 54 (26 to 84) Median duration of disease (range), years: 3 (0.5 to 35) Proportion of participants with psoriatic lesions elsewhere: not specified Withdrawal: 2 dropouts (1 because of flare‐up at other parts of the body, and 1 elderly participant because of illness)
Interventions	Intervention 1 A: Grenz ray therapy (4 Gy) once per week Intervention 2 B: placebo Co‐interventions: none Duration of treatment: 6 weeks
Outcomes	No primary or secondary outcome pre‐specified Improvement in score (based on a 5‐grade scale for erythema, itching, scaling, postulation, and distribution and on a visual analogue scale) Adverse events
Notes	Funding: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The nurse treating the patient gave the active radiation or placebo treatment according to a randomised predetermined code" Comment: no precision on how the code was generated
Allocation concealment (selection bias)	Unclear risk	Comment: no information on method to guarantee allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "double‐blind placebo‐controlled. Neither the patient nor the evaluating doctor knew which side had received active Grenz ray therapy" Comment: probably done, but nurse treating the patient was not blind
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "double‐blind placebo‐controlled. Neither the patient nor the evaluating doctor knew which side had received active Grenz ray therapy" Comment: probably done
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Quote: "Of the 17 patients who started the trial, 2 patients failed to participate throughout the study" Comment: no clear mention of how study authors deals with dropouts
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol found to guarantee that all planned outcomes are presented in the results