Going back to January 29, 1993 to yesterday (August 18, 2014), on an unadjusted basis, there have been 224 gap ups of at least 1 percent and 235 gap downs of at least 1%. Out of the 5,427 total trading days in the look-back period, this represents 4.13% and 4.33% of total trading days consisting of gap ups/downs of at least 1% on an unadjusted basis, respectively.
More interestingly, I decided to look at the percentage of time that SPY closed higher than where it opened on gap up days (at least 1%) and closed lower than where it opened on gap down days (at least 1%). When SPY gaped up at least 1%, it closed higher than where it opened 58.04% of the time. This compares to a 51.59% total (closing above where it opened). On the opposite end, when SPY gaped down at least 1%, it closed lower than where it opened 48.94% of the time, compared to a 47.13% total.
As you can see below, even when SPY gaps down at least 1%, the intraday performance (i.e., where it closes in relation to where it opens) has been positive, both on an average and median basis (0.09% and 0.06%, respectively). While the performance numbers themselves may not seem too impressive in magnitude, the fact that SPY has averaged out a positive median intraday positive performance going back to 1993 seems to suggest, on aggregate, buying strength (specifically, gap ups in excess of 1%) has been better than shorting gap downs in excess of 1%.
While this clearly isn't meant to serve as a trading strategy, I think it provides some insight into the historical performance of the market (specifically, SPY ETF). In addition, this rather truncated analysis doesn't provide any insight into the market structure (bear/bull market); this is another big component that needs to be considered as well.
Interesting nonetheless (at least for me, hopefully for you as well)!
|Gap Up, % Pos Close||58.04%|
|Gap Down, %, Neg Close||48.94%|
|Up, Avg Perf||0.22%|
|Up, Median Perf||0.29%|
|Down, Avg Perf||0.09%|
|Down, Median Perf||0.06%|