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Jack Pizza
look ahead bias in vix
Sanjeev Mittal
Fair point — two separate VIX issues in v1.0, now fixed in v1.1:
1. vix_pct_rank was computed over different-length windows in training vs live inference (full history slice in training, 100 bars in CheckSignal). Standardised to a fixed 252-bar window in both places so the model sees the same distribution it was trained on.
2. The 80th-percentile spike threshold for the dip-entry rule used only 100 bars (~5 months). In a low-vol regime that threshold can drop to ~12, classifying normal VIX as a 'spike.' Extended to 252 bars with a hard floor of 20.
No future price data leaked into labels — the training loop slicing is clean. These are distribution mismatch and threshold instability issues rather than classic look-ahead, but both would cause live/backtest divergence. Code updated in version notes.
QuantConnect Reconciliation
The material on this website is provided for informational purposes only and does not constitute an offer to sell, a solicitation to buy, or a recommendation or endorsement for any security or strategy, nor does it constitute an offer to provide investment advisory services by QuantConnect. In addition, the material offers no opinion with respect to the suitability of any security or specific investment. QuantConnect makes no guarantees as to the accuracy or completeness of the views expressed in the website. The views are subject to change, and may have become unreliable for various reasons, including changes in market conditions or economic circumstances. All investments involve risk, including loss of principal. You should consult with an investment professional before making any investment decisions.
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