In 15 states, 25 percent or fewer of those signing up for coverage through President Obama's health care law are from the crucial young adult demographic, according to an analysis of data from the Department of Health and Human Services.

Analysis of data from HHS
This is far below the 40 percent threshold White House officials initially said was required to ensure healthy insurance exchanges.

On Thursday, I reported that nationally, about 28 percent of those signing up through the exchanges were aged 18 to 34. But national numbers are only a rough indicator of the state of play on the exchanges, because in reality, the insurance market is made up of 51 different risk pools - one for each state, plus the District of Columbia.

For the law to fully succeed, there needs to be a critical mass of younger and healthier enrollees to offset the cost of covering older and sicker participants. And that critical mass needs to be achieved in every state. Otherwise, the price of insurance will soar, thus further discouraging those with fewer medical needs from purchasing coverage.

A further breakdown of the numbers reveals that a number of states did especially poorly in signing up younger participants. West Virginia was the worst performing state, with just 19 percent of sign-ups coming from the younger age group. In Hawaii, 20 percent were from the younger demographic. The percentage was 21 in Arizona and 22 in Oregon, Vermont, and Maine.

On the flip side, Washington, D.C., was the only exchange to exceed the original target of the Obama administration with 45 percent of sign-ups coming from the younger demographic, as it got a boost from a flood of Capitol Hill staffers who were required to get their insurance through the exchange. Utah was the next best with 33 percent of signups coming from the young adult population. All in all, 13 states were at 30 percent or higher.

HHS did not release data on the number of individuals who signed up for coverage who completed enrollment by paying their first month's premiums. If it turns out the non-payment rate is higher among younger adults, these numbers could end up worse.

It’s worth adding a few words of caution. The raw young adult enrollment numbers aren’t necessarily going to determine how insurers price plans. It’s quite possible to be old and healthy, or young and sick, so data on medical claims is important. It also is important how enrollment and medical usage tracks with insurer expectations. Some states have older populations to begin with and therefore insurers may have already priced their plans accordingly.