The number of data points is very important when trying to convince others (or yourself) that something is true.

There’s no particular evidence I’m looking for. I don’t have any issues with the conclusion (that active funds consistently underperform low-cost index funds), because I’ve seen plenty of other evidence and studies that show the same thing.

My issue is with the technique of showing one incidence of something happening and asking readers to come to the conclusion that it is likely to continue to happen.

That said, thank you for the book recommendation. I just took a look at it on Amazon, and it looks quite interesting.

The bottom line is that professional money managers – as measured by the performance of actively traded mutual funds – cannot outperform the major benchmark indexes. And even if they could, that 1 to 2% management fee would turn the fund into an under-performer.

I don’t have all the evidence at my fingertips, but for starters, try: The Great Mutual Fund trap by Baer and Gensler

To me, looking at several 20-year periods tells us a great deal more than looking at one 20-year period.

And I’d argue that it also provides more helpful information than simply saying “here’s what happened over the 80-year period from 1929-2008.” I don’t know many investors who are looking at 80-year time-frames.