Supporters of the DISCLOSE Act now have empirical evidence to back up their claims, thanks to a study published April in American Politics Research.

"Despite the rise of anonymity in political advertising, there has been little empirical work examining the effects of disclosure of donors on the persuasiveness of campaign advertising," researchers Conor M. Dowling of the University of Mississippi and Amber Wichowsky of Marquette University noted in the study.

The Democrat-backed DISCLOSE Act was crafted in response to the U.S. Supreme Court's Citizen United decision and the rise of so-called "dark money" groups, social welfare nonprofit organizations with overtly partisan objectives.

Social welfare nonprofits like Crossroads GPS are not required by law to disclose their donors, unlike Super PACS and other political committees, which must file regular reports with the Federal Elections Commission. Some versions of the DISCLOSE Act would require all these organizations to list their top donors at the end of political ads.

For their study, Dowling and Wichowsky had 1,213 participants watch a political attack ad from the 2010 Missouri Senate race. The ad was produced by American Crossroads, a Super PAC founded by Karl Rove and Ed Gillespie, and attacked Democratic candidate Robin Carnahan. After watching the ad, some participants received a list of donors while others read news articles about American Crossroads. The participants were then questioned about which candidate they supported.

The researchers found political attack ads were less effective when people were provided a list of the top five donors who funded it. Surprisingly, this only occurred when people were given a simple list of the donors and the amount they contributed. Reading a news article naming the top donors appeared to have no effect.

"Our study suggests that voters may be more likely to pay attention to campaign finance data if it is directly and objectively presented, much in the same way that nutritional information is displayed," Dowling and Wichowsky explained in the study.

Political attack ads, however, did become less effective after the participants read a news article about the donors being kept secret. In fact, knowledge that the organization behind the ad was keeping its donors secret had a greater negative impact than knowledge of the top donors.

"This result suggests that individuals and corporations could be viewed in a negative light if they do not disclose their donors, which is perhaps one reason why several corporations have decided either to not make political contributions or to adopt their own disclosure policies," Dowling and Wichowsky wrote.