Ben Bernanke might not be giving Trichet-style press conferences, but he is at least taking to the op-ed page of the Washington Post to explain yesterday’s decision. Here’s what he’s trying to achieve with his quantitative easing:

Easier financial conditions will promote economic growth. For example, lower mortgage rates will make housing more affordable and allow more homeowners to refinance. Lower corporate bond rates will encourage investment. And higher stock prices will boost consumer wealth and help increase confidence, which can also spur spending. Increased spending will lead to higher incomes and profits that, in a virtuous circle, will further support economic expansion.

I don’t think that lower mortgage rates are going to make housing more affordable: there’s no evidence that I can see that rents fall when interest rates drop. If anything, the opposite is true. And in the wake of being stung by predatory adjustable-rate mortgages in the past, most homeowners now have fixed-rate mortgages, which don’t get any cheaper when rates fall. Or, of course, they have no mortgage at all.

So there really only two groups of people who are affected by the lower mortgage rates. One is homebuyers. Their numbers have shrunk to historic lows. And the other, as Bernanke explicitly says, is people refinancing their mortgages. But this round of QE isn’t going to bring mortgage rates down to levels significantly lower than they’ve been in the recent past: anybody liable to refinance on lower mortgage rates is likely to have done so already. So the rolls of potential refinancers are pretty thin as well.

Bernanke lists two other positive effects of QE, though. The first is that “lower corporate bond rates will encourage investment” — a statement contingent on the idea that there are firms out there who would love to borrow money to invest, but they find the interest rate they would have to pay to issue bonds too damn high. I can’t think of any companies like that, and so this effect, too, is going to be decidedly marginal.

Finally, Bernanke gets into very dangerous territory indeed: he explicitly says that he’s trying to boost stock prices. Surely if we’ve learned anything from Greenspan’s mistakes it’s that the Fed shouldn’t be trying to support stock prices, and that attempts to do so are liable to end in tears.

Meanwhile, although Bernanke says that “the FOMC has been cautious, balancing the costs and benefits before acting”, he only mentions one cost, inflation — and that cost he mentions three times. He doesn’t even hint at other costs, such as increased market uncertainty and volatility, or increased currency-related difficulties as investors pile in to the global carry trade.

It’s also odd that Bernanke is talking down the risk of higher inflation given that, as Brad DeLong says, the only way that QE is going to work is if it results in higher inflation expectations. In a piece of clever math, DeLong calculates the value to the market of the Fed’s interventions at just $7 billion a year, which clearly isn’t enough to move an economy the size of the US. “Unless this moves inflation expectations in a serious way, it is hard to see why they came out here,” he concludes.

So while I welcome Bernanke trying to explain his actions in the form of an op-ed, I’d be much happier if he did so in the form of a press conference, or some other place where people could ask him questions. He’s good at communicating; why doesn’t he use those skills better?

Felix Salmon is an Audit contributor. He's also the finance blogger for Reuters; this post can also be found at Reuters.com.