Maybe I didn’t explain myself clearly above. Although Merced is not a highly selective campus, its posted admission rate doesn’t tell the whole story.
As some background: When a student applies to UC, they check a box for each campus they are applying to, at a cost of $80 per campus.
If a student is eligible for the statewide guarantee (top 9% in the state) or ELC guarantee (top 9% in the student’s high school), the student knows that they will automatically be offered admission to a UC campus, if they aren’t admitted to any of the campuses they choose. Therefore, many students feel that they don’t actually have to apply to Merced and pay the $80 fee. Merced acts as an automatic safety school for them, without even applying, as long as they applied to at least one other UC campus.
Also, many students in CA who are applying to OOS or private schools have a tendency to apply to just a couple of reach campuses in the UC system, for example, to UCLA and UCB, or perhaps to those two along with UCSD, etc. These students may not be interested in Merced at all, but if they are not admitted to the reach campuses where they applied, they will be auto-admitted to Merced (there is no way to “turn this option off” in the UC application).
All in all, over 200,000 students apply to UC each year, but only about 25,000 of these students are paying $80 to explicitly apply to Merced.
Students who are auto-admitted to Merced, but did not apply to Merced, are counted in the numerator, but not the denominator, of the posted acceptance rate. This artificially increases the posted acceptance rate, which is why the rate can go over 100%.
(Note that at this time, my understanding is that some students are being offered Riverside instead of Merced, so this is also going to affect the Riverside acceptance rate. However, in the past, the guarantee meant that you would be offered Merced.)