Justification of Delphi methodology~The Delphi method has been widely used for elaboration of guidelines. The goal of the Delphi method is to solicit group opinion and to combine the opinion of a panel of experts into a consensus (or dissensus). During a Delphi study, multiple rounds of questionnaires are sent to a panel of experts with feedback between rounds, allowing experts to re-evaluate their responses along with the replies of other experts.~Design, expert eligibility and data collection A steering committee of members of the French Centre of Evidence (G. Chaby, F. Corgibet, L. Fardet, S. Leducq, F. Poizeau https://reco.sfdermato.org/fr/centre-de-preuves-en-dermatologie) and members of the Psoriasis Research Group of the French Society of Dermatology (M. Chastagner, L. Gouillon), without any competing interest regarding this topic, will be in charge with elaboration and conduction of the Delphi study.~The selected experts will be asked whether they agree to participate in the Delphi survey. Upon acceptance, they will be asked to answer the Delphi study administered using the online survey Welphi®. Before the first round, demographic information (age, sex, location of practice, availability of a phototherapy cabin, public or private practice) and competing interests will be collected. All experts will provide informed consent. Experts will have 2 weeks to complete the online survey with two email reminders. For each round, the number of experts who completed the surveys will be documented.~Procedure~Definition of consensus For statements with responses on an ordinal 7-point Likert scale (rating 1, strongly disagree to 7 strongly agree), 'agreement' will be defined as a score of 5-7, 'neutral' by a score of 4 and 'disagreement' by a score of 1-3. Consensus will be defined as achieved when > 70% experts will vote for a given option on the Likert scale. For Multiple Choice Questions (MCQs), consensus will be defined as achieved if > 70% experts voted for a particular option. Median and interquartile range (IQR) will be used to describe the central tendency and dispersion of responses: a strong statement will be defined as a median score of ≥ 6 or ≤ 2 on the Likert scale and 90% votes for MCQs. If consensus is not reached for one question (using Likert scale or MCQ) after 3 rounds, dissensus is acted. For this study, four rounds are planned, including round 1 with open-ended questions (see below) and a maximum of three rounds to obtain consensus.
French guidelines on the use of systemic treatments for moderate-to-severe psoriasis in adults have been developed by the psoriasis research group of the French Society of Dermatology using literature available until July 2017 (Amatore et al, 2019). Because several systemic treatments have been marketed since then, new guidelines are mandatory. The aim of this study coordinated by the Centre of Evidence of the French Society of Dermatology is to update the available French guidelines using a Delphi method.