WHEN A LACK OF CREDIBILITY MEETS FUZZY MATH…. It’s difficult to do too much in the way of budget scrutiny when it comes to House Budget Committee Chairman Paul Ryan’s 2012 plan, because he hasn’t published all the relevant data. But the far-right Republican has shared his plan with some analysts, who’ve run the numbers.

Unfortunately, those analysts work at the Heritage Foundation.

The Republican budget’s economic projections are rosy, including growth rates of over 3 percent for the next three years. An analysis performed by the Heritage Foundation at Ryan’s request found the unemployment rate would be reduced to 4 percent in 2015 by Ryan’s budget, an incredibly low number when many economists believe the economy will not return to so-called “full employment” of about 5 percent until years after that.

Well, rates nearing full employment by 2015? Where do I sign up to endorse this magical proposal?

Wait, it gets better. Heritage also believes the unemployment rate will drop to 2.8% by 2021, just so long as we do exactly what Paul Ryan wants us to do.

There’s obviously no way any sensible person would take this seriously, but so long as Ryan and Heritage are touting these fantastical numbers, it’s probably worth noting a couple of relevant details.

For one thing, an unemployment rate of 2.8% is almost certainly impossible, and the notion of 4% unemployment by 2015, created by a massive effort to take public investment out of the economy, is laughable on its face.

For another, both Ryan and Heritage have a very bad track record, leaving them with no credibility on the subject at all. It was Heritage, for example, that assured us that Bush’s tax cuts would generate an economic boom and the near elimination of the federal debt (instead of the reality of an economic crash and an additional $5 trillion in debt). And it was Heritage and Ryan who were convinced that the 2009 Recovery Act would fail to improve the job market and prove unsuccessful in generating economic growth.

In other words, with so much on the line, it’s probably best not to listen to those who’ve been so wrong for so long their rhetoric is literally unbelievable.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.