I’m not sure about that, @hzhao2004.
Yale historically has allocated about 40% of total admits to the SCEA pool. I think Yale cares about yield management to some degree, so on balance would lean toward giving a higher percentage of total admits to SCEA applicants because they’re more likely to matriculate (by applying there early rather than anywhere else, they’ve indicated that they favor Yale).
That said, though, I think the SCEA applicants Yale accepts are the ones Yale both (i) knows would be admitted anyway (so doesn’t need to wait to see if there are better versions of them in the RD pool) and (ii) really doesn’t want to lose, e.g., recruited athletes and superstars in their categories (so wants to show them love by admitting them early). I’m aware of several legacies who were deferred SCEA and ultimately admitted RD, and I have to think it’s because Yale knows they’re very likely to accept an offer whenever it comes and doesn’t want to “waste” an SCEA admit on them.