## Traders' Roundtable

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Testing quantitative trading strategies is necessary, but difficult. There is the danger of data snooping — that **trading testing software,** thinking that the best of a large number of tested strategies is better than it really is.

Another danger is to find the same thing that lots of others have found. August showed how hazardous that can be. Random portfolios can help relieve both of these problems. They give you more stringent criteria with which to accept a strategy. They also allow you to see more ephemeral signals, and hence help you avoid doing what everyone else is doing.

A backtest starts with some initial portfolio at the start of the time period. Trades use the reputedly market-beating signal while obeying a set of constraints. The result is a return over the period. We can learn the significance of that return by imitating the backtest but leaving the signal out.

We start with the same initial portfolio, trading testing software do random trades throughout the period that obey the constraints, but pay no attention to the signal. QQplot of performance percentiles. It is not good practice to use just one starting portfolio — you could be the victim of either good or bad luck. Figure 1 shows a strategy performance relative to random paths for twenty different starting portfolios.

A performance percentile of 0 means that no random paths did better than the backtest, means all random paths did trading testing software. In this case there is a slight indication that the strategy is doing something positive.

That there are a lot of points at the extremes indicates the strong power of the method. Once you have a sense that the strategy truly outperforms, you want to know by how much — is it trivially trading testing software or seriously outperforming? A plot like Figure 2 can help you with that. This looks at the trading testing software return minus the mean of the returns of the random paths. Figure 2 is plotting the mean of that across the twenty runs. Figure 1 is for the first quarter 0fso at day This technique need not be limited to backtests.

You can use it in real-time as well to see how your trading testing software is currently performing. Portfolio Probe Burns Statistics Investment technology for the 21st century. Data basics Add benchmark to variance matrix Example data Prices to returns Read a comma-separated file into R Read a tab-separated file into R Returns to variance matrix 2. Generate Random Portfolios Asset limits Create and plot valuations Give a range for turnover Returns and realized volatility Very simple long-only Very simple long-short Volatility and tracking error constraints 3.

Optimize Trades Active with benchmark Active, no benchmark Asset allocation Asset limits Compute a technical indicator Control turnover Create and plot trading testing software valuations Dollar neutral and general case Impose transaction costs Minimum variance with tracking error constraint Passive with benchmark minimum tracking error Passive, no benchmark minimum variance Realized portfolio returns and volatility Scenario optimization First four moments utility Generate historical scenarios Generate statistical trading testing software Maximize the omega ratio Maximize value Write your own utility function Write optimization results to a file 8.

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