Why are odds changed?
Once placed on the bookmakers’ sites, odds are constantly changed and there is a number of objective reasons for this.
Usually, bookmakers show the lines for an event few days before it. This time varies depending on the various sports and leagues. If the sport and the teams are not very popular, then it is possible that the odds are shown few hours before the event starts. It is also possible that a bookmakers doesn’t show an event at all since he doesn’t have enough information about it. In fact, not many bookmakers can afford to maintain their own “odds compiler” – employees and money used for the analysis of sports information and the determination of odds. This service is usually done by specialized firms and the bookmakers receive ready lines for the sports events. However, as soon as the odds are posted, they are changed by the bookmakers. Each bookmaker sets different margins and has a specific betting model. Some bookmakers underestimate the favorite, overestimate the underdog, and others do the exactly opposite, there is a different attitude towards the circulation of the Draw option and so on. “The Opening Lines” – the first odds to be shown, are yet to be changed depending on various factors until the start of the event.
We can divide the factors which influence the odds into 2 main groups - sporting technical and marketing. To the first group we can assign all factors taken into consideration by the odds compiler and changed after the generation of the lines. These changes usually concern the members of the teams. It is possible that an injured player for whom it was not planned to take part in the event improves his health. If he is a key player this would objectively change the balance of the game. Sometimes, a team member could suffer an injury or fall ill before the start of the game which would also change the balance of the game. What is more, teams could undergo dynamic changes since team members could be suspended or get back in the game after a suspension. All changes in the positions of the team members, even rumors about eventual changes, as well as any information for upcoming transfers could influence the state of the team members and their motivation.
A change in weather conditions could also greatly influence the predicted results of the sport event. For instance, bad ground conditions would decrease the effectiveness of a football match, weaken the technical abilities of the players and diminish the difference between the favorite and the underdog. These circumstances lead to a significant change of the chances of a team and the odds.
Undoubtedly, the sporting technical information gives objective basis for defining the chances of the teams but, in practice, it is possible that the odds are changed under the influence of marketing tools. There are often events with an obvious favorite and the bets are mostly placed on its victory. The main responsibility of every bookmaker is to gain a balanced distribution of the bets on the various betting options. If there is an imbalance, the bookmaker diminishes the odds for the most preferred outcome. By doing so he is making this betting option less interesting to the players. You should notice that in every situation the bookmaker keeps his margin, i.e. if he decreases the odds for one option, he increases the others with the idea to increase the bets on those options. The flexibility and timely reaction of the bookmaker rules out or at least minimizes his risk.
Sometimes bookmakers have to keep up with common marketing trends in odds movements.
In spite of the changes of the odds, the bets that have already been placed are not changed.