3.2 Theory of Odds Movements
As we have been told in previous lessons betting odds is a reflection of the money you may win and the assumed implied probability to win.
It is necessary to separate odds movement analysis in two main periods, which are:

Before the kick off

During the game
The parameters related to odds movements are different between these two periods.
Before the kick off
In general terms betting odds publish weeks before a football game. It is a long period before the kick off and many things can change during that period.
One parameter that may move the odds up or down is the change of the implied probability to win or not during the period before the kick off. Announcements of team’s news, player’s injuries, people’s public opinions etc may change the probability of the event and may cause bookmakers to move the odds.
A second parameter that may cause bookmakers to move the odds is the liquidity of betting transactions in betting markets.
For example, if the majority of punters bet on Home team to win and nobody bet on Away or on Draw, bookmakers must move the odds to make Away and Draw markets more attractive for betting. In that case, they have to reduce the odds of the Home win and to increase the odds for Away and Draw.
If bookmakers don’t make these corrections of the odds, they will not achieve an added value between betting transactions and they may lose money.
During the game
Only the inplay progress of the game (goals etc) is related to the odds movement during the game.
One parameter that causes bookmakers to move the odds is the elapsed time.
For example let’s take the market U2.5 goals:
Let’s assume U2.5=1.8 at Elapsed 1min, that means probability = 1 / 1.8 = 0.55 or 55%
After 30min at Elapsed = 30min if there is no goal the probability for the game to finish with less than 2.5 goal is probably more than 55%.
So, if we assume a probability equal to 70% at elapsed 30min, then the odds must be U2.5= 1 / 0.70 = 1.43.
Bookmakers calculate the assumed probabilities during the game and change (move) the odds.
A second parameter that causes bookmakers to move the odds is goals.
For example let’s take the market U2.5 goals:
Let’s assume U2.5=1.8 at Elapsed 1min, that means probability = 1 / 1.8 = 0.55 or 55%
If a goal scored at 10min, then the probability for the game to finish with less than 2.5 goals is probably lower than 55%.
So, if we assume a probability equal to 30% at elapsed 10min, then the odds must be U2.5= 1 / 0.30 = 3.33.
A third parameter that causes bookmakers to move the odd is the game itself.
If one team plays much better than the other one and it seem they are going to win, then the odds may vary very quickly for the favorite.