In recent years, Sport Select has come under increasingly heavy criticism from Canadian gamblers due to the poor odds it offers (from the gambler's perspective). A private bookmaker licensed in the United Kingdom or Nevada generally maintains an overround (or "vig") of about 110%, meaning the bookmaker can expect to pay out $100 for every $110 that is wagered. In Canada, however, the overround for an individual match in Sport Select odds often exceeds 130%. To make matters worse for the bettor, the parlay requirement compounds the overround - the actual vigorish is a minimum of 160% but can climb to well over 300% (if six selections are made).
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This represents the odds against each, which are 4-6, 1-1 and 4-1, in order. These values now total 130%, meaning that the book has an overround of 30 (130−100).
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This is why bookmakers offer bets such as Lucky 15, Lucky 31 and Lucky 63; offering double the odds for one winner and increasing percentage bonuses for two, three and more winners. In general, for any accumulator bet from two to i selections, the combined percentage overround of books of B1, B2, ..., Bi given in terms of decimals, is calculated by B1 × B2 × ... × Bi × 100 − 100\. E.g. the previously mentioned fourfold consisting of individual books of 120% (1.20) gives an overround of 1.20 × 1.20 × 1.20 × 1.20 × 100 − 100 = 107.36%.
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This represents an implied probability of 29.752% (1/3.3611) and multiplying by 4 (for each of the four equally likely combinations of outcomes) gives a total book of 119.01%. Thus the overround has slightly more than doubled by combining two single bets into a double. In general, the combined overround on a double (OD), expressed as a percentage, is calculated from the individual books B1 and B2, expressed as decimals, by OD = B1 × B2 × 100 − 100\. In the example we have OD = 1.0909 × 1.0909 × 100 − 100 = 19.01%. This massive increase in potential profit for the bookmaker (19% instead of 9% on an event; in this case the double) is the main reason why bookmakers pay bonuses for the successful selection of winners in multiple bets: compare offering a 25% bonus on the correct choice of four winners from four selections in a Yankee, for example, when the potential overround on a simple fourfold of races with individual books of 120% is over 107% (a book of 207%).
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Wholesale odds are the "real odds" or 100% probability of an event occurring. This 100% book is displayed without any bookmaker's profit margin, often referred to as a bookmaker's "overround" built in. A "wholesale odds" index is an index of all the prices in a probabilistic market operating at 100% competitiveness and displayed without any profit margin factored for market participants.
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Traders can make money by betting exclusively with betting exchanges or bookmakers, or by combining the two. The trader could lay at a low amount on a betting exchange and then back at a higher price with a bookie or another exchange. This must be done simultaneously to guarantee a profit or else the opportunity could quickly cease to exist with liquid markets quickly correcting prices and bookies trying to avoid being arbitraged. Most exchanges post the book percentages (colloquially known as the overround or "vig") prominently for each market.
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In gambling, Dutching is sharing the risk of losing across a number of runners by backing more than one selection in a race or event. One needs to calculate the correct stake to place on each selection so that the return is the same if any of them wins. Although not foolproof, because handicapping is still involved, there have been successful bettors throughout history who have applied this system. This is not to be confused with what constitutes a Dutch book which is when a bookmaker goes overbroke (the opposite to overround).
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As a rule, bookmakers do not want to have a financial interest creating a preference for one result over another in any given sporting event. This is accomplished by incentivizing their clientele to wager offsetting amounts on all potential outcomes of the event. The normal method by which this is achieved is by adjusting the payouts for each outcome (collectively called the line) as imbalances of total amounts wagered between them occur. Within the mathematical disciplines of probability and statistics this is analogous to an overround, though the two are not precisely synonymous but rather bijective reciprocals of one another.
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An odds compiler may be required to monitor the financial position the bookmaker is in and adjust their position (and odds) accordingly. They may also be consulted as to whether to accept a bet or not, usually in the case where a very large bet is being placed, so as to not incur dangerously-high liabilities. Odds are usually not set completely independent from other bookmakers but are influenced by what others are quoting. This is particularly important when the overround is below 100% and hence arbitrage betting, where betters can make a profit regardless of the outcome, is possible (see mathematics of bookmaking).
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Some small bookmakers and startups purchase software from specialised white label solution providers. Since gambling products have a high conversion rate from one niche to another, most online betting websites also feature other gambling products such as poker, live dealer casino games, lottery, bingo, slots and other casino games. Controversially, the explosion in Internet gambling is being linked to a rise in gambling addiction, according to the UK's help and advice organisations for addicts, GamCare and Gamblers Anonymous. Increasingly, online bettors are turning to the use of betting exchanges such as Betfair and BETDAQ, which automatically match back and lay bets between different bettors, thus effectively cutting out the bookmaker's traditional profit margin also called an overround.
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It is customary with fixed-odds gambling to know the odds at the time of the placement of the wager (the "live price"), but the category also includes wagers whose price is determined only when the race or game starts (the "starting prices"). It is ideal for bookmakers to price/mark up a book such that the net outcome will always be in their favour: the sum of the probabilities quoted for all possible outcomes will be in excess of 100%. The excess over 100% (or overround) represents profit to the bookmaker in the event of a balanced/even book. In the more usual case of an imbalanced book, the bookmaker may have to pay out more winnings than what is staked or may earn more than mathematically expected.
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However, a bookmaker would probably offer odds of 5-6 (for example) on each of the two possible outcomes in each event (each tennis match). This results in a book for each of the tennis matches of 109.09...%, calculated by 100 × ( + ) i.e. 9.09% overround. There are four possible outcomes from combining the results from both matches: the winning pair of players could be AC, AD, BC or BD. As each of the outcomes for this example has been deliberately chosen to ensure that they are equally likely it can be deduced that the probability of each outcome occurring is or 0.25 and that the fractional odds against each one occurring is 3-1. A bet of 100 units (for simplicity) on any of the four combinations would produce a return of 100 × (3/1 + 1) = 400 units if successful, reflecting decimal odds of 4.0.
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When a punter (bettor) combines more than one selection in, for example, a double, treble or accumulator then the effect of the overround in the book of each selection is compounded to the detriment of the punter in terms of the financial return compared to the true odds of all of the selections winning and thus resulting in a successful bet. To explain the concept in the most basic of situations an example consisting of a double made up of selecting the winner from each of two tennis matches will be looked at: In Match 1 between players A and B both players are assessed to have an equal chance of winning. The situation is the same in Match 2 between players C and D. In a fair book in each of their matches, i.e. each has a book of 100%, all players would be offered at odds of Evens (1-1).
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