Firedave trading Betfair with Bet Angel

BetFair is pretty close to being an efficient market however, it is not totally efficient. There is always an element of error due to the ever changing opinions and money going through the markets. The most efficient time is the start of the race as all money to either back or lay has been matched at this point. This doesn't make it the best time to trade though, the market can change violently just before the start.  This is because traders are trying to get out of their positions in the last few seconds before the off and any trend that may have formed will be disrupted. This is another reason to make sure you are out of the markets at this point and not to let it go in-play.

The book overound is a piece of information we get from BetFair and will vary according to the number of runners. What value will my "efficient market" be? Well, each runner should produce 0.1% error/margin/profit so you should expect a book as follows:

12 runners = 100% + (12 x 0.01%) = 101.2%

4 runners  = 100% + (4 x 0.01%)   = 100.4%

When the book is moving towards 100% then something is going to have to shorten in price to push the book back towards efficiency and likewise if it is moving towards the upper limit something will have to drift to pull it back into line.

The move to correct the book usually revolves around the favourite as that is where most of the money is. A collective drift or steam on multiple runners can have the same effect but if you watch the favourite's price you won't go wrong too often.  This isn't a piece of information you can use on its own but does help give some confirmation when making a decision to enter, or exit a trade.  This is a good indicator when there is only one clear favourite in a race. When there are multiple favourites, it is unclear which runner will move to correct the book.