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Cathy wrote:
I couldn't readily find a link, but I'll take a shot. At least this is how I've always calculated an SOS ranking, so I hope others will jump in and correct me if I'm wrong. It's actually quick and easy enough to just do on paper.

Take the two screens you'd like to blend, in this case, Up_5% and Value_at_the_Top. List the top ten stocks for each screen. Give each stock in one screen a rating, beginning with 10 for the top stock, 9 for the second, etc. Do the same for the second screen. Finally, add up the score for each stock, and select the four highest rated. If there are no overlaps between the two screens, this will end up being the top two stocks from each screen. When a stock appears on both screens, their scores should be combined, potentially causing it to outrank one of the top two.

For this week, using the rankings provided so generously by Bill2m, the four stocks would be VIRT, BXC, DQ, and RYCEY. There were no overlaps between the stocks appearing in the top 10 positions for each screen, so the SOS just grabbed the top two for each.

Well, that is the way the FlyingCircus coded it for GTR1. And don't forget that Jamie has included a SOS Backtest in backtest.org. Here are the instructions from backtest.org for building a SOS, which match up with Cathy's explanation.

Choose which screens to select the stocks from. You may limit choices to stocks that appear on some minimum number of screens or unique screen categories (i.e. Keystone, RS, etc.). Note that the concept of "unique" only applies to a limited subset of the predefined screens.

The stocks in each screen are ranked, counting down from the first stock to the specified position (or all stocks if no position is specified). The first stock gets max points (max defaults to position), the second max-1, and so on. The totals for each stock are then sorted, and the highest limit stocks are chosen. In the case of a tie, a secondary sort is done by looking at each screen in sequence, and selecting the stock that appears first.

Another popular SOS tool is the Saucer, which allows you to generate a list of current rankings for SOS combinations

Note that there are other ways of breaking ties (see http://boards.fool.com/barrydto-for-selection-purposes-now-i..., which is also covered in the Dummies manual).

Charlie