Here are some numbers from 1990 onward:
Total of 75 days of over 4% gains on the NDX.
The following day breaks down like this:
1990-2000
13 up days, average gain 1.56%
12 down days, average loss -1.674%
2000 to present
23 up days, average gain 2.54%
27 down days, average loss -2.38%
The last 5 days following a 4% up day have been up days.
Funny enough, last July 5th we were up 4.14% and on July 8th, we were down 3.51%. I hope history repeats itself.