You can find the entire message here:On another forum Palmer Wright wrote:Leslie Walko points to the potential danger of curve fitting caused by compounding. I agree, and have been concerned for years about how one market in a portfolio (commodity X) by being dramatically profitable in a single year can misleadingly bias the results of the whole portfolio.
During a multi-year test in TR, starting equity is low, perhaps $100,000, but compounding raises equity to many million in later years. The one-year outperformance of commodity X cand produce two kinds of curve-fitting bias: early-years bias and end-years bias. Mark Johnson's message describes the first, where X gives "a big turbocharged boost" to the portfolio's equity, which then gives a head-start boost to the number of trades in all the commodities traded. The second occurs when X's monster trades occur in the final years of the simulated time period when the large number of contracts makes X's profit far larger than if its big year came early. Here the profits contributed by X dwarf what they were in the first case.
As the message from M points out, we can avoid such biases by normalizing with a fixed-dollar bet size in testing to remove the galloping equity effect. I proposed this method in 1999, and still use it to compare with the compounded performance. I confess, however, that my testing has failed to find as much performance bias as I suspected I would find. The method is most important when selecting markets for a portfolio.
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