Baran 1999a.

Methods	This was a double‐blind, internally placebo‐controlled study. In the methods of the trial, no randomisation is mentioned. We assume the study was randomised because the comparable trial in the same publication (Baran 1999) was randomised. It was unclear if intention‐to‐treat analysis was conducted.
Participants	Inclusion criteria of the trial The trial included 18 participants who had fingernail psoriasis affecting both hands (all of the participants were men; age range = 22 to 79 years; average age = 53.7 years). During the study, 3 participants dropped out, and 15 participants were evaluable.
Interventions	8% clobetasol‐17‐propionate in a colourless nail lacquer vehicle Placebo lacquer The participants applied the placebo lacquer to 1 hand and the clobetasol lacquer to the other hand once daily in the first week and from the second week onwards twice or 3 times weekly. The nail lacquer film was removed with a cosmetic nail varnish remover once weekly before a new application. The duration of treatment ranged between 5.1 and 8.9 months (average duration = 7 months).
Outcomes	Outcomes of the trial Therapeutic results on a 4‐point scale: cured, improved, failure, or worsened Observed features: onycholysis. pitting, subungual hyperkeratosis, salmon patches, splinter haemorrhages, ridging, transverse grooves, onychomadesis, and periungual psoriasis
Notes	The trial required participants who had been treated with intralesional steroids to have a wash‐out period of more than 2 months.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Each participant was treated randomly."
Allocation concealment (selection bias)	Unclear risk	Comment: The paper provided insufficient details.
Blinding (performance bias and detection bias) Clinician/ Investigator	Low risk	Quote: "...double‐blind study."
Blinding (performance bias and detection bias) Participants	Low risk	Quote: "...double‐blind study."
Blinding (performance bias and detection bias) Outcome assessor	Low risk	Quote: "...double‐blind study." Comment: The blinded clinician was probably the assessor.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "18 participants who had fingernail psoriasis affecting both hands were included, three dropped out during the study. At the end of the study, 15 participants were evaluable."
Selective reporting (reporting bias)	Low risk	Comment: All of the outcomes were reported.
Other bias	Low risk	Comment: This was free of other sources of bias.