C-SPAN had previously released their 2021 Presidential Historians Survey.
Surveys are distributed to historians, professors and other professional observers of the presidency who are drawn from databases of C-SPAN programming, research in the field and suggestions from our academic advisers. Each cycle, we reach out to past participants and add new names to the list to maintain a well-rounded list of invited participants. This year, 142 completed the survey, up from 91 in 2017.
All former presidents are graded based on the sum of all the averages of each of the ten ‘individual leadership characteristics’ that are each graded by all the participants in the survey from 1-10 which are each converted to 10-100 rating (lowest is 100, highest is 1,000 for ‘total’ final score when all the averages are added together):
Read the full survey here: https://www.c-span.org/presidentsurvey2021/?page=overall