Originally posted on 05/18/2011:

To expand upon what TFG said, consider -110 lines, which have an implied probability of 52.38%. The no-vig line is +100, which has an implied probability of 50%. If a market was perfectly efficient, each side of matchup that closed at -110 / -110 would win 50% of the time. Therefore, if you got -105 on one of the sides and then it moved to -110, you would have beaten the VIG closer but not the NO VIG closer. Your bet is still -EV because you would have paid the price of something with a 51.22% implied probability when its actual probability was 50%.