NEW YORK TheStreet ) -- Investors have been dumping actively managed mutual funds and shifting to passive choices that track benchmarks such as the S&P 500. Plenty of academic researchers support the move, arguing that most active funds lag the indexes. Now an active fund company is fighting back. American Funds, which oversees $1 trillion in assets, has published a report that makes the case for active management. Conceding that average funds trail, the company argues that some special managers win consistently. The report notes that it is a mistake to conclude "that because the average person cannot dunk a basketball, no one can dunk a basketball." To support the case, American Funds cites the returns generated by its equity funds from 1934 through 2012. The study examines rolling returns. To calculate the rolling 10-year returns, you start by tallying results from 1934 to 1943, then you consider data from 1935 through 1944, and so on. In 73% of the 10-year periods, the funds topped the benchmarks. In 98% of 30-year periods, the company outperformed. Funds that beat the benchmarks in 100% of 30-year periods include American Funds Fundamental Investors ( ANCFX), American Funds Growth Fund of America ( AGTHX) and American Funds Washington Mutual ( AWSHX). American Funds has achieved its impressive long-term results by following a careful investment strategy. The company focuses on buying rock-solid stocks when they are somewhat out of favor. The approach has excelled in downturns and about matched the benchmarks during bull markets. American Funds has maintained its performance over decades by carefully training portfolio managers and giving them incentives to stay. Few managers ever quit, and many of the current staff have been with the company for more than 20 years. Confronted with the success of American Funds and other companies, some passive investors scoff and claim that the returns can be attributed to luck. But in the case of American Funds, the record is so long and consistent that it is difficult to dismiss the results. No other company can match the seven-decade record of American Funds. Still, there are some competitors that have consistently excelled over long periods. Among the best performers are Baron, Oakmark, Mutual Series, and T. Rowe Price. These companies all have many funds that have topped their category averages during the past 10 years. The active managers have excelled by developing disciplined approaches for maintaining strong results over long periods. Odds are good that these funds can keep delivering winning results.