Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Psoriasis improvement
Systematic review	49 people with severe psoriasis Data from 1 RCT	Clearance (complete resolution of at least 90% of psoriasis) 19/30 (63%) with suberythematous UVB + tar oil 14/19 (74%) with maximally erythematous UVB + emollients	ARR –0.11 95% CI –0.37 to +0.1 The RCT was underpowered to detect clinically important differences between groups		Not significant
RCT	22 people with severe psoriasis, bilateral study (two sides of the body treated differently)	Response rates with tar oil plus suberythemogenic doses of ultraviolet B radiation with oil vehicle (an emollient) plus suberythemogenic doses of ultraviolet B radiation	The RCT found no evidence that adding coal tar to UVB improved response rates. However, it was underpowered to detect clinically important differences between groups		Not significant