Here's a paradox of the U.S. economic recovery: credit-card borrowing remains roughly 30% below its precrisis level, even though revolving loans are cheaper than they've been in at least six years.

Those findings come from a new report by the American Bankers Association. The report looks at credit card borrowing as a percentage of disposable income, as well as the effective finance charge yield on credit card accounts.

Both metrics are at or near their lowest levels since early 2008, according to the report. In the fourth quarter of last year, Americans' credit card debt outstanding equaled 5.4% of their disposable income. That was down from 7.7% in the first quarter of 2008.

The effective finance charge yield, which measures card issuers' interest income as a percentage of average daily balances, sat at 11.1% in the third quarter of 2013. The same metric was at 12.7% during the first three months of 2008.

Ken Clayton, executive director of the ABA's card policy council, says that Americans hadn't seen an economic event as scary as the financial crisis in generations.

"I think that stamps an imprint on people, about taking a more conservative approach to debt," he says. "And I think that lasts beyond the immediate cycle."

The report, embargoed for release on Wednesday, sheds light on other potential contributors to the industrywide trends.

One reason why borrowing costs have fallen is likely the fact that issuers have become much more reluctant to offer credit to less creditworthy customers. Because those customers are more likely to default, they tend to pay higher prices when they borrow.

Subprime borrowers had total credit lines of $352 million in 2009, but that number plunged to $202 billion in 2013, according to the report. Meanwhile, super-prime borrowers saw their total credit lines rise from $1.54 trillion in 2009 to $1.70 trillion last year.

One likely contributor to the sharp fall in credit-card borrowing is the fact that U.S. consumers have become more likely to pay off their entire balance each month. Account holders who pay in full each billing cycle accounted for 19% of all customers in the first quarter of 2008. By the third quarter of last year, their share had risen to 28.6%, according to the report.

Clayton says the steep fall in credit-card debt outstanding is the result of greater prudence by lenders and borrowers, and he doesn't expect big changes in the trend during 2014. "I don't think you'll see dramatic shifts," he says.

Despite the fall in credit-card borrowing, U.S. consumers are more prone to use plastic to make purchases than they were during the recession, the report found. The data showed a bounce back in monthly credit-card purchase volume that likely reflects a recovery in consumer confidence and overall consumer spending.

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