What is relevant? The number of total admits and the ... size of the EA pool admitted versus the spots available for enrollment. THOSE are comparable metrics of selectivity.
And those numbers are apparently known and expected to be as true as the typically released numbers from Chicago.
The "delta" values at HYPS are substantially higher than they are for MIT/Chicago. For instance, HYP early success was in the 15-20 percent range, with overall rates of 6 or 7 percent. Thus, the early-to-overall ratio at HYP was about 3:1. At Stanford the ratio was a bit over 2:1 (about 11 percent early/5 percent overall). By contrast, MIT admitted about 9 percent early and 7 percent overall, while Chicago admitted about 11 percent early and 8.5 percent overall. The EA-to-overall deltas are less than 1.5, and well below those at HYPS. Of course, the numbers themselves don't tell the whole story.
Nonetheless, my view is that as a matter of tactics, there is a stronger incentive to apply early to an SCEA school as compared to a non-restrictive EA school.