ad 1)
The system (pairs trading model) decides automatically when to open long pair position (leg #1 long, leg #2 short) or short pair position (leg #1 short, leg #2 long). Details are here:
https://wiki.pairtradinglab.com/wiki/Pair_Trading_Modelsad 3)
I want to be more specific here and I will provide an example. Right now, while opening pair position, the system takes the margin for the pair position and splits it in equal halves. Then, for each half it buys as many stocks as possible. This is determined by current instrument price only.
Example with Visa and Mastercard:
https://www.pairtradinglab.com/backtests/VNN_VV007C2o1XI72014-06-17 NYSE:V Sell 210.81 2.314 1 23
2014-06-17 NYSE:MA Buy 74.98 2.314 1 66
When you take a look on the first trade, you can see it opened 23 shares of Visa vs 66 shares of Mastercard. So it
already does the balancing you mentioned (1 Visa to 3 Mastercard) automatically - based on trading price of both instruments.
You can also make this decision based on a different indicator, like
beta. Then it uses estimate beta to do the balancing, instead of just using the open prices. This can go to slightly different results - depends on actual difference between estimated beta and ratio of prices.
So actually, when using different ratio than the ratio of prices for weighting both positions, you are introducing some additional bias to your pair trade. I will think about introducing the possibility of having fixed custom weighting in the backtester. But I think this is something for advanced pair traders.
Hello and thanks again for your answers.
1. Could you please tell me where the system points out which underlying is long?
2. That answers my question completely.
3. OK - 1 Visa to 3 Mastercard contracts, for example. That would be very interesting. Glad to read that you are thinking of adding this.