Quote from amitkumar_ny:
I noticed v303 calculating differently too. I asked Jared and he said they modified the code to only look at 1 year data in v303 to avoid software from crashing. He thinks this number is better or more informative. I don't know what to make of the whole thing. I am running DFuller tests in matlab as well and it does seem that cointegration moves a lot based on near term data. e.g. SAIA / XTN was a great pair and both CADF and PTF numbers calculated higher COINT. Recently (past couple of weeks) the pair has gone to hell and CADF test says they are not co-integrated any more. PTF v301 agrees and shows 13% cointegration. So it works but if you get in on a pair and it goes to fell and cointegration number falls off do you get out ? or wait to see if comes back. Half life of this pair is like 12 days so do you wait ?
That is the same question that I have. Wait or not wait - after the co-integration value of a pair plunge. From my prospective if the value fluctuates wildly from day to day then the backtest for finding pairs becomes irrelevant and unreliable. The PTF pairs determined today will not be the same tomorrow if the of value of the pairs fluctuates dramatically. After all we are looking for pairs that move in almost tandem fashion for a duration of time to capture the discrepancy when they are of whack. It also means you need to re-run the back test every week or so to determine the new pairs. The value will change but should not be dramatic. From my understanding for the value to have meaning the look back day should not be too long and not too short. I don't know what the optimal value should be. Maybe 90 days to 120 days?
After all, there is a discrepancy in v301 and v303. Now I wonder why I was told they should be the same. BTW, how responsive is Jared with your questions? I had to wait for almost a week to get a response (that is after repeated emails!). Hopefully, this time I do not have to wait a week again. Needless to say it is frustrating.