This question allows for some gray area. Letter writers need to be objective, so letters from professional colleagues with close personal relationships with the applicant are discouraged. Specifically ...

The nominators, with input from candidates, will submit to the administrative coordinator for the Robertson Award names of individuals whom they would like to write letters of recommendation ... peers ...

If you are applying to more than one graduate program, we highly suggest you contact your recommendation providers and encourage them to write all-inclusive letters of recommendation that support your ...