Article Note: Funding sources: this investigator-initiated study was conducted with financial support from Almirall. The funding source had no influence on study design, data collection and analysis, or the content of the manuscript. Conflicts of interest: M.E.C.v.W. has carried out investigator-initiated research with financial support from Almirall and has conducted clinical trials for AbbVie, Celgene, Janssen, Leo Pharma, Lilly and Novartis. E.L.M.t.H. has carried out investigator-initiated research with financial support from Almirall and has conducted clinical trials for Novartis. P.C.M.v.d.K. served as the chief medical officer of the International Psoriasis Council and received fees for lectures and consultancies from Bristol Mayer Squib, UCB, Leo Pharma, Eli Lilly and Company, Dermavant, Almirall, Celgene Novartis, Janssen and AbbVie. E.M.G.J.d.J. has received research grants for the independent research fund of the Department of Dermatology, Radboud University Medical Centre, Nijmegen from AbbVie, Pfizer, Novartis, Janssen Pharmaceutica and Leo Pharma, has acted as consultant and/or paid speaker for and/or participated in research sponsored by companies that manufacture drugs used for the treatment of psoriasis including AbbVie, Janssen Pharmaceutica, Novartis, Lily, Celgene, Leo Pharma, UCB and Almirall. All funding is not personal but goes to the independent research fund of the Department of Dermatology at Radboud University Medical Centre Nijmegen, the Netherlands. S.F.K.L. has received research grants for investigator-initiated research by Almirall.