I have been fortunate to observe the PhD admission process in both Stanford and Harvard for several of their physical sciences programs. For 3 years, I assisted in reviewing some of the applications for selected candidates before the graduate open house. Getting an offer into one of these PhD programs is exceedingly competitive. The selection process might seem opaque for an outsider, but here I try to demystify the process on how PhD committees select their candidates.
The admissions selection process relies upon a number of interconnected factors on deciding who gets an offer! All applications are initially screened administratively (not by professors) based on the applicant’s academic and test scores (GPA+ GRE). Schools employ different formulas on how to average the two but eventually applications that don’t make the cut are weeded out. In top US programs, typically around ~30% or so of the applications make it to the next stage, where professors are the arbiters on the final decisions. Graduate committees are comprised from 4-6 professors from different fields covering the main research areas in the department. Each professor or committee member is assigned a set of applications to review. If the applicant specified a research subject in his/her application, it will be reviewed by the relevant professor whose expertise covers this area. This ensures that your background/research experience will be evaluated by someone who is well-informed on the topic, its relevancy, trends, and the top researchers in the field.
Applications are usually reviewed by two committee members and gets both 1- numerical score from each one and 2- short few-sentence review of the application. The review is descriptive of the main strengths and weakness of the potential candidate, i.e “great reference letters, average GRE”, or “substandard grades but excellent GRE”. The score is usually given a scale (e.g. 0-5, 1-10, etc.) with 5 or 10 reserved for the highest ranked candidates. It is important to note that the score is based on the reviewer overall perception of the candidate, taking all factors (grades, GRE, letters, Ug schools, …etc) into account. The average reviewer score is then used for deciding the fate of the application. Outstanding candidates are then signaled out in a different pile, and then are considered for more prestigious fellowships.
In the beginning of the review process, it is often difficult to assign accurate scores to potential candidates since this score is weighted by the quality of the entire pool of applications. Committee members, thus, often go back and recalibrate their scores after going through all their assigned applications. All final decisions are made during the committee meeting after some discussions on the quality of this year pool compared to previous ones. Despite these careful measures, there are often cases where the same application gets contrasting reviews. This happens when the two committee members differ in their respective evaluation of the candidate, i.e if the applicant gets a 8-9 from one member and 5 from another. These differences are sorted out by debate and discussion during the final admissions committee meeting. In these discussions, applications that might have otherwise got rejected (due to low average reviewer score) can get rescued by a committee member who has a strong case for admitting the candidate. The final selection process is thus a time consuming and complicated one. However, it receives due diligence from every committee member since maintaining an excellent quality of incoming students is a high priority for any top tier graduate school.