Last week I discussed the importance of net win vs. expected value when looking at wagers of different sizes.  The term expected value was originally used mostly to describe video poker hands.  Since the wager size is the same from hand to hand and the payouts are all essentially odds based - meaning they pay a certain amount for each unit wagered as opposed to a fixed dollar amount, using the expected value works fine.  But, in a game like blackjack where the Player has the option to double down, we need to look at net win (or loss) and not expected value.  We lower our win frequency (which lowers the expected value) when we double down, but we still do so because in the end we win more money, which is the real goal.