Hi Howard, Just a very simple question. Or perhaps not ... Which of the three on page 320 of EBTA described solutions for dealing with data-mining do you prefer : a.. Out of Sample testing with the WalkForward, b.. Bootstrapping/MonteCarlo or c.. Deflating the observed performance with 'Markowitz Correction Factor'. Regards, Ton.
----- Original Message ----- From: Howard B To: [email protected] Sent: Tuesday, October 06, 2009 6:40 PM Subject: Re: [amibroker] Re: Is the Walk forward study useful? Greetings all -- There has been a lot of activity on this thread. I'll not respond to each point individually, but will make a couple of general comments. I know David Aronson, speak with him regularly, and collaborate with him on projects. I have a copy of his book, "Evidence-Based Technical Analysis." His book is excellent and I highly recommend it. I think David and I are in pretty close agreement on most of the modeling, simulation, testing, and validation issues. I have spoken with Robert Pardo and have exchanged several emails and forum postings with him. I think his earlier book was very good, particularly at the time it was published. And his more recent book is not quite up to those standards. There are several important areas he did not cover and several areas where I see things considerably differently than Robert. I have spoken with and exchanged emails with Van Tharp, and I have copies of his books "Trade Your Way to Financial Freedom" and "Definitive Guide to Position Sizing." Both are excellent, and I recommend them both highly. Be sure to get the second edition of Trade Your Way to Financial Freedom -- it has some important corrections and clarifications. Permit me a short rant on my soapbox. I really dislike it when people claim ownership of common terms. Tom DeMark, Robert Pardo, Van Tharp, and others put Service Mark symbols on terms that they think are unique to them, but are not. I appreciate Tharp's enthusiasm over what he calls System Quality Number, but I wish he would not put the Service Mark symbol next to every occurrence of it. And trying to Service Mark the term Position Sizing is like a dietician service marking "calorie counting." Robert Pardo claims "Walk Forward." I used exactly that term describing exactly that process in research papers I delivered at conferences in the late 1960s. The mark has been registered, not by Robert, but by a company I used to work for and with which Robert was not associated, over my strong objection. End of rant. System quality number is equivalent to t-test. Systems with SQNs above 2 work well for exactly the same reasons that systems with t-test scores above 2 work well. In fact, it is possible to create a custom objective function that Is the t-test and use it for optimization. Attendees at my workshops in Melbourne later this month will see that demonstrated. Optimizing for the t-test of expectancy is equivalent to optimizing for CAR, so don't bother creating the custom function unless you have a better candidate for your objective function than CAR. Back to the topic at hand ----- There is No rule of thumb to determine how long the in-sample period should be. The Only way to determine that is by testing the model and the data together. And be prepared for that length to change over time. Some writers suggest a relationship between the number of free parameters and the number of data points, or some proportional division of the available data. Those techniques do work on industrial time-series data which is usually stationary, but they do not work on financial time-series data which is non-stationary and changes as trading systems become better at extracting inefficiencies from it. No matter how good the in-sample results look, no matter how high the t-test score is, no matter how many closed trades are represented -- in-sample results have no value in estimating the future performance of the system. None. The only information you have that gives any indication of future performance are the out-of-sample results from testing on data that was never used at all -- not even once -- during system development. Tomorrow is out-of-sample. The only way to prepare for real-money trading tomorrow is to be rigorous during the system testing and validation process. Anything less will overestimate the probability of success. Thanks for listening, Howard
