Custom Opinion fields can be added by clicking on the Plus button in the (Global) Fields manager, and selecting the option Opinion scale in the dropdown menu.
The event organizers can edit the name of the field (e.g. How likely are you to [...]), the label for the field which is visible to contacts and participants (which may or may not be the same as name of the field), and the category the field belongs to (e.g. Personal information).
You can select the maximum value available (5,10, etc.), and the default value when the contact/participant first opens the page.