dcfox83

One of them (the most successful for me at least) is the semi-strong form efficiency with regards to earnings releases...

On average, any positive or negative impact of an earnings release gets incorporated in the stock as thus (i may be a bit off on the actual numbers but they are in the CFAI book)

~35% before the date of the earnings release (due to investor expectations, whispers etc.)
~15% on the day of the release
~50% afterwards..

if that happens on the average, why not make some money of it when it doesn't happen that way ;)

Stock splits, lawsuits others have their own impact