It hasn't always gone down after earnings announcements. If you look at q3 2014 and q4 2015 they were exceptions. Other quarters in 2013 & 2014, were also exceptions so it is really about 75 percent up and 25 percent down with no respect to beats vs. misses.
So far, the recent trend has been down after earnings announcements (last 4 quarters), but maybe it is about to break that trend as it has been show to in the past after a series of down trends after earnings announcements.
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