The new all=time intraday high Friday for SPX came on a day when NDX had its worst day in over a year. There has never been another time where SPX made a 200-day intraday high while NDX had its worst drop of the last 200 days. Loosening the criteria to a 50-day high for SPX and the biggest drop in 50-days for NDX there have been 5 instances.
Too few occurrences to put much confidence in an edge, but the limited results are fairly impressive. I note that every instance had a run-up of at least 5%, and the largest drawdown was under 3.2%.
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