@williams2021, you are comparing Swarthmore’s overall (ED + RD) yield with Williams’ RD yield.
Using your analysis, here are the numbers for Swarthmore last year (from their CDS):
of Applicants: 7717
of RD accept: 774
of ED accept: 214
of students joining from last year gap year: ?
Class size expected: 400 (ish?)
Swarthmore admitted 774 students hoping to fill the rest of their class. 400 - 214 = 186.
Which equates to a 24% yield for RD.
Williams overall yield last year was 45%. (1230 admitted, 553 enrolled)
When you compare apples to apples, Williams has a slightly higher yield.