How much is a picture of a smiling woman worth?

For men receiving loan offers in the mail, the answer is 4.5 percentage points.

Dean Karlan, a microfinance expert and economics professor at Yale University, cited some unusual study findings in a keynote address at the fourth annual Underbanked Financial Services Forum here in Dallas on Monday: men who received a mailed loan offer that included a picture of a woman (from the neck up, for the record) were as likely to take out the loan as men who were offered one with a rate that was 4.5 percentage points lower.

The conference, which is presented by the Center for Financial Services Innovation, an affiliate of ShoreBank Corp. in Chicago, and SourceMedia Inc., the parent company of American Banker, continues through tomorrow.

Karlan also co-founded That Web site threatens to give your money to friends or foes - including, depending on your political inclinations, the Bill Clinton Presidential Library fund or the oil and gun lobbies - if you don´t meet the goals you set on the site. (Popular examples include weight loss and quitting smoking.)

On Monday, he described how the use of sticks and carrots can influence consumers´ financial behavior - their willingness to save money, repay debt, or to use certain banking products or services.

Hence the smiling woman in the loan-offer mailings. Her marketing power, while diminished, did not completely disappear with female recipients. According to the same study, women who received the same offer for a loan with the picture of the woman were as likely to accept it as those women who received an offer of a loan with a 2.2-percentage point lower rate.

It´s not quite a thousand words, but it'll do.