The Problem with Back Testing Investing Strategies for Practical Investors
In surveying some of my favorite blogs recently, I have come upon something that hadn’t previously occurred to me, but could potentially alter how I invest. That is the problem with back testing Investing Strategies. Greenbackd posted an interesting starter piece on this subject called Walking the Walk, that led me back to the original blog from Aswath Damodaran called Transaction Costs and beating the Market. I have often thought there were practical problems with back testing, but I had not tried to articulate them until I read these posts. Both are excellent and worth reading. Damodaran, who is a Finance professor at NYU, and an author of Investment Fables (which I own), writes about the many ways to beat the market in general terms and then goes on to say, “Most of these beat-the-market approaches, and especially the well researched ones, are backed up by evidence from back testing, where the approach is tried on historical data and found to deliver “excess returns”.
Ben Graham’s Stock Selection Criteria – Value Investing Series
I found this idea in Tweedy Browne’s What Has Worked in Investing. And after a little more research I have included it in my Value Investing Series. In a “Test of Ben Graham’s Stock selection Criteria,” Henry Oppenheimer studied whether or not a set of Ben Graham’s investing criteria actually worked. Toward the end of Graham’s life he espoused a different, although related criteria to what he espoused in his master works Security Analysis and the Intelligent Investor.
80-20 Investing and Other Financial Heresies
I am slowly developing, over time, an investment method I call 80-20 Investing. Everyone knows the 80-20 rule. For any activity you spend 20% of your time to get 80% of the result. The converse is obviously also true. The last 80% of effort only yields a 20% result. I really don’t want to waste my time, so I am interested in maximum efficiency.
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