I wonder if there are any correlations between up days during market leading to gains after hours or maybe the opppsite, down days leading to gains after hours. Something to take the after hours bias and perhaps isolate conditions where it is even more likely to be.
In the decades that I have been trading, our group of traders (family and friends) use to keep track of the correlation between:
1: Pre-market futures Up: Dow= +100 Dow / SP500= +10,
versus closing prices on that day;
Bull Market= closed Up 70% (or >) of the time. /
Bear Market= closed Down < 50% of the time.
2: Pre-market futures Down: Dow= -100 Dow / SP500= -10,
versus closing prices on that day;
Bull Market= closed Up > 50% of the time. /
Bear Market= closed Down 70% (or >).
These studies we did were based on at least a decade containing both a bull & bear market.
The problems with blinding using this kind of data is, these were long term averages that dramatically changed depending if we were in a Bull or Bear Market.
In others words:
1: In a Bull market your odds of an Up close with strong positive pre-market futures are in your favor, but those odds are not in your favor in a Bear market.
2: In a Bear market your odds of a Down close with strong negative pre-market futures are in your favor, but those odds are not in your favor in a Bull market.