Why do bookmakers change their odds?
Odds will change if the book is trying to balance out the money being laid on either side. For example, if the public favours one team in a football match too much, the odds will change to attract support to the other team. If you see the odds change significantly, the public may be responding to a situation you are not aware of, like an injury. Or it might simply be one team, player or horse is overly popular.
