A key to being persuasive is to provide concrete details, rather than abstract generalities, and the information doesn’t necessarily have to be in written form. Spoken words also can influence behavior.

Psychologists Eugene Borgida and Robert Nisbett presented information differently to two groups of college students, prospective psychology majors who were considering whether to enroll in certain courses. They presented the information differently to each group.
Group A received statistical summaries of how students had rated courses on a written evaluation. Group B, in a different room, sat before a panel of students, who rated the courses orally.
Participants in the face-to-face presentation were more affected by the information they heard directly from other students, even though the panel contained far fewer people than the group that had provided written evaluations.  Students said they were less likely to take a course if they had heard critical comments about it from a panel member.
The oral testimony was more persuasive because it was more concrete than statistical information.