Invitation "policy" is not the same as invitation "process" or "schedule". The policy is, 'we interview 30-40%, and admit 10-15% overall'. Other schools might interview less and admit more interviewed applicants; or interview more and admit less applicants.
The schedule or process (which is what I was referring to) is however a different thing altogether. At Wharton, an application goes through multiple reads, and multiple people give their input on whether a candidate gets interviewed. Just because of this reason (that it must be read multiple times by different parties), it takes longer than a process where a single adcom member reads it, and can he/herself decide whether to interview the applicant.
So why do we do it this way? At Wharton, the first read is typically done by a student, and the second by an adcom member. We like students to give input on every aspect of the school (curriculum, clubs, everything)- and this includes admissions. That should give you an indication of how strong this culture of "student co-production" is.
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