https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6937988/#CR22

Thought to provide insight into applicants’ non-cognitive traits, letters of recommendation written on behalf of applicants can grasp the attention of selection committees. An online survey completed by program directors, chairpersons, and members of resident selection committees from 65 United States ophthalmology residency programs showed that 83% of programs considered letters of recommendation to be among the most important component of applications []. It has also been demonstrated that letters of recommendation were the most important factor for screening and evaluating applicants for medical schools, graduate programs, psychology faculty positions, internships, and military training programs [–]. Selection committees rely on letters of recommendation to provide information on applicants’ motivations, qualifications, and past performances, and to reinforce the information provided by the applicants themselves [–].