Pure magic, or just an illusion?

Doesn't look like 30.8% to me

Greenbackd has an excellent round up of recent evidence on the outperformance of Joel Greenblatt's so called "magic formula".

I won't repeat his post - just go and read it.  But basically, it outperforms, but nowhere near the 30.8% cumulative annual growth rate that Greenblatt reported in his book.  Wes Gray has elsewhere noted that Greenblatt has dropped that number from his speeches.  Gray suspects that Greenblatt made an error in his backtesting.