Perhaps CNN’s in-house doctor, Sanjay Gupta, ought to stick to things medical. Gupta’s attempt to explain John McCain’s health plan offered a confusing and ultimately misleading picture of how the candidate’s proposals might work. McCain, you may recall, has proposed giving every family a $5,000 tax credit and every individual a $2,500 credit to help buy insurance policies in the commercial market. So it was reasonable for Gupta’s show to ask: How far will five grand really get you? Too bad it didn’t answer the question.

Gupta began by citing a study done a couple of years ago by America’s Health Insurance Plans (AHIP), the insurance industry trade association. Gupta was wrong at the outset when he called AHIP “the largest provider of health insurance.” AHIP is a lobbying organization for its insurance company members. It does not—does not—provide health insurance. Gupta said AHIP had found that the average family’s premium was $5,799; he didn’t say that the data had been collected two years ago, and he didn’t explain that any study done by an insurance trade association is necessarily of limited value. (In fact, no organization has adequately studied the so-called individual market, where McCain wants people to buy their policies with his tax credit.) The take-away for viewers, though, was that a family could buy a policy for the amount offered by McCain’s tax credit.

Gupta did note a couple of other caveats, but missed the mark in explaining them. He reported that premiums vary depending on where you live, saying that family premiums cost about $16,000 or so in Massachusetts and $3,000 in Wisconsin. That allowed him to segue into McCain’s proposal for letting insurers sell across state lines—in effect, picking and choosing states with lax business regulations. The implication was that you might be able to buy a cheap policy in Wisconsin if McCain’s plan became law. But people in Massachusetts might have better consumer protections than those in Wisconsin, which they might lose in their quest for cheaper premiums. Gupta didn’t talk about that.

He did say that the premium “depends on the individual in terms of pre-existing conditions. These health care costs can vary widely if you’ve had some sort of illness before.” Premiums (not health care costs) might increase 50 percent or more if an insurer offers a policy at all. But the main point is that many sick people don’t get coverage in this market. Gupta skipped right over it.

Instead he jumped into territory he should have avoided—a comparison of the individual market and the employer market, where most people get their insurance. He told viewers that another organization, Kaiser (Kaiser Family Foundation), says that the average family premium from employers is around $12,000 a year, much higher than the $5,800 cited in the insurance industry study. Gupta gave this reason:

When an employer covers people they pool a lot of people together, people who are otherwise healthy and people with pre-existing conditions and that does tend to drive up cost.

I asked a neutral insurance expert, Paul Fronstin, who directs research for EBRI, the Employee Benefit Research Institute, to translate Gupta’s wonk talk. Fronstin said Gupta “gives a gross oversimplification” that “implies that the individual market is filled with healthy people, and that’s why the premiums are lower, because only healthy people are covered. Companies don’t have to raise premiums to cover the expenses of those who are sick.” This is far from an apples-to-apples comparison. The benefits, the regulation, and the people in the two markets are emphatically not the same, Fronstin explained.

Trudy Lieberman is a fellow at the Center for Advancing Health and a longtime contributing editor to the Columbia Journalism Review. She is the lead writer for The Second Opinion, CJR’s healthcare desk, which is part of our United States Project on the coverage of politics and policy. Follow her on Twitter @Trudy_Lieberman.