Twice a year the S&P publishes a report called SPIVA, which is a scorecard to see how mutual funds, aka active portfolio managers, are faring versus their passive index funds. SPOILER ALER: Active management is getting killed. The SPIVA report even controls for other variables such as style drift, survivorship bias, and avoids double counting different share classes of the same fund. This makes SPIVA the most accurate and reliable performance data available in the Active vs. Passive debate.