Many economists, Ben Bernanke foremost among them, have argued that monetary policy has effects that are independent of the traditional interest rate channel (where an increase in the money supply lowers the real interest rate and induces more investment and consumption spending). The alternative models include a "credit channel" for monetary policy, which is often further divided into financial accelerator models and bank lending channel models.
One class of models within the bank lending channel branch relies upon a difference in the availability of credit for large and small firms. If smaller businesses have fewer sources of credit than large firms (who can issue bonds, stocks, commercial paper, etc.), then a credit shock induced by policy or some other factor will have an asymmetric negative effect on the activity of large and small firms. Since smaller firms have trouble getting credit from non-bank sources, a disruption in bank credit can cause them to contract their activities much more than large firms. (If all firms have perfect substitutes for bank credit, e.g. borrowing from foreigners on the same terms, then monetary policy cannot affect real output through the bank lending channel. The point of this research is that some firms do not have close substitutes for bank credit, and therefore monetary policy can have real effects.) According to this, there's some evidence that these effects are operable:
Credit Tightens for Small Businesses, NY Times: Many small and midsize American businesses are still struggling to secure bank loans, impeding their expansion plans and constraining overall economic growth...
Bankers worry about the extent of losses on credit card businesses as high unemployment sends cardholders into trouble. They are also reckoning with anticipated failures in commercial real estate. Until the scope of these losses is known, many lenders are inclined to hang on to their dollars rather than risk them on loans to businesses in a weak economy...
Bankers acknowledge that loans are harder to secure than in years past, but they say this attests to the weakness of many borrowers rather than a reluctance to lend.
“Banks want to lend money,” said Raymond P. Davis, chief executive of Umpqua Bank, a regional lender based in Portland, Ore. “The problem is the effect that the recession is still having on us. Some of these businesses are still trying to come out of it. For them to go to a bank, if they are showing weak performance, it is harder to borrow.”
As the financial crisis has largely eased in recent months, big companies have found credit increasingly abundant, with bond issues sharply higher.
But for ... many smaller companies,... borrowing remains tough. ...
Recall this graph posted here not too long ago (discussed further at the source):
It may be hard to see at first glance, but the graph shows the "disproportionate effect the recession has had on very small businesses." In 2001, only 9% of the job losses came from small businesses, while in the current recession - where credit problems are a much larger factor - small business accounts for 45% of lost jobs. Part of the discussion of the graph notes this comment from William Dudley, the president of the Federal Reserve Bank of New York:
In a speech yesterday,... he said:
"For small business borrowers, there are three problems. First, the fundamentals of their businesses have often deteriorated because of the length and severity of the recession—making many less creditworthy. Second, some sources of funding for small businesses—credit card borrowing and home equity loans—have dried up as banks have responded to rising credit losses in these areas by tightening credit standards. Third, small businesses have few alternative sources of funds. They are too small to borrow in the capital markets and the Small Business Administration programs are not large enough to accommodate more than a small fraction of the demand from this sector."
It will take more careful analysis to make the case that the bank lending channel has been important in this recession, but it is suggestive.