The purpose of this randomized, open label, crossover, single site study is to compare the PISs of two Multiple Sclerosis clinical trials to elucidate potential aspects of the given written information that could impact on the smooth running of the studies.

The participation to a clinical trial is based on two forms of information: the spoken information, usually given by a clinician during the enrolment meeting, and the written information, reported on the Participant Information Sheet (PIS). Numerous studies performed to improve and enhance informed consent, have used different methods to evaluate the quality of the given information such as: interview, checklist, questionnaire, readability formulae. Even if these tools can be useful, they show evident limits in detecting the real efficacy of the proposed consent form in terms of the patient's comprehension.

User Testing (UT) is a method originally developed in the 1990 in Australia, to assess how a text about medicinal products performs with its intended users and not just its content.

Generally, the UT is based on an iterative 4-step process in a cohort of participants (the target group):

• individual reading of the text;
• individual questionnaire for a quantitative and qualitative evaluation;
• a brief semi-structured interview to each participant;
• a text revision to address any problems identified from participant feedback; Then the revised document is tested again with a second cohort and this iterative process continues until all issues with the document are resolved. However, a methodological issue not yet explored is whether the UT could be used to compare two different PISs, in order to elucidate aspects that could be involved in improving or worsening the understanding of a PIS.

UT has been recently used to evaluate the PIS belonging to phase I and phase III clinical trials (CT) in Myeloid Leukemia, immunomodulatory therapy and for poor responders in vitro fertilization. To date, in no case the UT method has been tested in patients affected by chronic disease like Multiple Sclerosis (MS).

We want to apply the UT approach to highlight the critical issues and communication difficulties present in PISs used in MS clinical trials.

Inclusion Criteria: PwMS (60%) and Caregivers (40%):

for PwMS:

• 18 years or older;
• MS diagnosis according to McDonald criteria;
• Informed consent to the present study for caregivers:
• 18 years or older;
• in being a person who takes care of a PwMS;
• Informed consent to the present study

Exclusion Criteria:

- not having taken part in one of the following trials evaluated in the present study: A) Observational Study of the Prevalence of CCSVI in Multiple Sclerosis and in Other Neurodegenerative Diseases (PIS-A); B) BRAin VEnous DRainage Exploited Against Multiple Sclerosis (PIS-B).