Outside groups spent more money than candidates in at least 10 of the nation's hottest congressional races last year, a university think tank reported Monday.

In a Pennsylvania House race between two incumbents -- Republican George Gekas and Democrat Tim Holden -- outside groups spent twice as much as the candidates did, a study by Brigham Young University's Center for the Study of Elections and Democracy found.

While Holden and Gekas together raised roughly $3 million, with about $1.5 million going to Holden and $1.3 million to Gekas, outside groups poured more than $7.5 million into the race, the study showed. Though most of it -- about $5 million -- was spent to help Gekas, Holden won.

The contest was among a handful of incumbent-vs.-incumbent House matchups around the country caused by redistricting.

The other nine races in which outside spending outpaced candidate spending in the last election included Senate races in Arkansas, Missouri and New Hampshire and House races in Arizona's 1st District, Colorado's 7th District, Iowa's 2nd District, Minnesota's 2nd District, New Mexico's 2nd District and for South Dakota's at-large representative, the study found.

The outside spending reviewed by the center included money that interest groups dedicated to issue ads and direct candidate support, as well as issue ads that political party committees aired in the districts at election time using "soft money," unlimited contributions from unions, businesses and others.

Many of the outside groups employed sophisticated campaign strategy, using polls and paid media, telephone and mail consultants, the researchers found.

Groups spending the most for congressional candidates independent of their campaigns in the last election cycle included the National Right to Life Political Action Committee, nearly $2.3 million; the American Medical Association PAC, about $1.9 million; and the Service Employees International Union PAC, $1.8 million, the study found.

The study chronicled what may have been the last election in which the national party committees could spend soft money.

A new campaign finance that took effect Nov. 6 prohibited the national parties from raising or spending soft money, and also restricted election-time political ads aired by interest groups. Several groups are suing to try to overturn the soft money ban and new ad limits, arguing they are unconstitutional.