Richard Dale
Norgate Data
- Joined
- 22 February 2005
- Posts
- 276
- Reactions
- 206
Norgate Data does do not sell, or provide, lists of historical index constituents on a date-wise point-in-time basis.
Skate,
Are your backtest results posted in the last several dozen posts baesd upon "point-in-time" constituents, or "current-constituents-at-the-time-of-posting projected to prior periods"?
Pre-inclusion bias is using today’s index constituents as your trading universe and assuming these stocks were always in the index during your testing period. For example if one were testing back to 2004, GOOG did not enter the S&P500 index until early 2006 at a price of $390. But your testing could potentially trade GOOG during the huge rise from $100 to $300.
People often write about systems they have developed using the current Nasdaq 100 or S&P500 stocks and have tested back for 5 to 10 years. Looking at this table shows that one should completely ignore those results. The difference between the two results is scary. Using the current list would make one think that they had a great system but actuality it was much worse.
So, all of your multi-year backtests that have used the "current" constituents are flawed. Other backtests that use only a small recent data set are also flawed (small sample size, recency bias, selection bias to name a few issues). Using a data set with survivorship bias/pre-inclusion bias for backtesting an algorithmic trading system is inaccurate, and will result in false and misleading conclusions.
I've made a switch to the dark side
My decision was a snap decision yesterday, but I had been thinking about the switch for a while.
Although flawed backtests may not yield perfect or definitive conclusions, they can still offer valuable insights.
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