Dictionary Definition
odds
Noun
1 the probability of a specified outcome [syn:
likelihood, likeliness] [ant: unlikelihood, unlikelihood]
2 the ratio by which one better's wager is
greater than that of another; "he offered odds of two to one" [syn:
betting
odds]
User Contributed Dictionary
English
Pronunciation

 Rhymes: ɒdz
Etymology
plural of odd 'uneven, strange'Noun
Translations
the ratio of the probabilities of an event
happening to that of it not happening
 Dutch: de kansen
 Finnish: todennäköisyys p
the ratio of winnings to stake in betting
situations
Derived terms
See also
Extensive Definition
 For the alternative rock band, see Odds (band).
In probability
theory and statistics the odds in favour
of an event
or a proposition are
the quantity p / (1 − p) , where p is the probability of the event or
proposition. The odds against the same event are (1 − p)
/ p''. For example, if you chose a random
day of the week, then the odds that you would choose a Sunday would
be 1/6, not 1/7. The odds against you choosing Sunday are 6/1.
These 'odds' are actually relative probabilities. Generally, 'odds'
are not quoted to the general public in this format because of the
natural confusion with the chance of an event occurring being
expressed fractionally as a probability. Thus, the probability of
choosing Sunday at random from the days of the week is
'oneseventh' (1/7), and although a bookmaker may (for his own
purposes) use 'odds' of 'onesixth' the overwhelming everyday use
by most people is odds of the form 6 to 1, 61, or 6/1 (all read as
'sixtoone') where the first figure represents the number of ways
of failing to achieve the outcome and the second figure is the
number of ways of achieving a favourable outcome: thus these are
"odds against". In other words, an event with m to n "odds against"
would have probability n/(m + n), while an event with m to n "odds
on" would have probability m/(m + n).
In some games of chance, this is also the most
convenient way for a person to understand how much winnings will be
paid if the selection is successful: the person will be paid 'six'
of whatever stake unit was bet for each 'one' of the stake unit
wagered. For example, a £15 winning bet at 6/1 will win '6 x £15 =
£90' with the original £15 stake also being returned.
Taking an event with a 1 in 5 probability of
occurring (i.e. a probability of 1/5, 0.2 or 20%), then the odds
are 0.2 / (1 − 0.2) =
0.2 / 0.8 = 0.25. This figure (0.25) represents
the stake necessary for a person to win one unit on a successful
wager. This may be scaled up by any convenient factor to give whole
number values. E.g. If a stake of 0.25 wins 1 unit, then scaling by
a factor of four means a stake of 1 wins 4 units. If you bet 1
at these odds and the event occurred, you would receive back 4 plus
your original 1 stake. This would be presented in
fractional odds of 4 to 1 against (written as 41, 4:1, or
4/1), in
decimal odds as 5.0 to include the returned stake, in craps payout as 5 for 1, and in
moneyline odds as +400 representing the gain from a 100
stake.
By contrast, for an event with a 4 in 5
probability of occurring (i.e. a probability of 4/5, 0.8 or 80%),
then the odds are
0.8 / (1 − 0.8) = 4.
If you bet 4 at these odds and the event occurred, you would
receive back 1 plus your original 4 stake. This would be presented
in fractional odds of 4 to 1 on (written as 1/4 or 14), in decimal
odds as 1.25 to include the returned stake, in craps as 5 for 4,
and in moneyline odds as −400 representing the stake
necessary to gain 100.
Gambling odds versus probabilities
In gambling, the odds on display do not represent the true chances that the event will occur, but are the amounts that the bookmaker will pay out on winning bets. In formulating his odds to display the bookmaker will have included a profit margin which effectively means that the payout to a successful punter is less than that represented by the true chance of the event occurring. This profit is known as the 'overround' on the 'book' (the 'book' relates to the oldfashioned ledger that wagers were recorded in and thus gives us the term 'bookmaker') and relates to the sum of the 'odds' in the following way:In a 3horse race, for example, the true chances
of each of the horses winning based on their relative abilities may
be 50%, 40% and 10%. These are the relative probabilities of the
horses winning and are simply the bookmaker's 'odds' multiplied by
100 for convenience. The total of these three percentages is 100,
thus representing a fair 'book'. The true odds of winning for each
of the three horses is Evens, 64 and 91 respectively. In order to
generate a profit on the wagers accepted by the bookmaker he may
decide to increase the values to 60%, 50% and 20% for the three
horses, representing odds of 46, Evens and 41. These values now
total 130, meaning that the book has an overround
of 30 (130 − 100). This value of 30 represents the amount
of profit for the bookmaker if he accepts bets in the correct
proportions on each of the horses. The art of bookmaking is that he
will take in, for example, £130 in wagers and only pay £100 back
(including stakes) no matter which horse wins.
Profiting in gambling involves predicting
the relationship of the true probabilities to the payout odds. If
you can consistently make bets where the odds of paying out are
better (pay out more) than the true odds of the event, then over
time (in theory) you will come out ahead.
The odds or amounts the bookmaker will pay are
determined by the amounts bet on each of the respective possible
events. They reflect the balance of wagers on either side of the
event, and include the deduction of a bookmaker’s brokerage fee
(“vig” or vigorish).
Even odds
The terms 'even odds', 'even money' or simply 'Evens' imply that the payout will be 'oneforone' or 'doubleyourmoney'. Assuming there is no bookmaker’s fee or builtin profit margin, this means that the actual probability of winning is 50%. The term “better than even odds” looks at it from the perspective of a gambler rather than a statistician. If the odds are Evens (11), and you bet 10, you would win 10. If the gamble was paying 41 and the event occurred, you would make a profit of 40. So, it is better than Evens from the gambler’s perspective because it pays out more than oneforone. If an event is more positively favored to occur than a 5050 chance then the odds will be worse than Evens, and the bookmaker will pay out less than oneforone.In popular parlance surrounding uncertain events,
the expression "better than even" usually implies a better than
(greater than) 50% chance of the event occurring, which is exactly
the opposite of the meaning of the expression when used in a gaming
context.
The odds are a ratio of probabilities; an
odds
ratio is a ratio of odds, that is, a ratio of ratios of
probabilities. Oddsratios are often used in analysis of clinical
trials. While they have useful mathematical properties, they
can produce counterintuitive results: in the
example above an event with an 80% probability of occurring is four
times more likely to happen than an event with a 20% probability,
but the odds are actually 16 times higher on the less likely event
(41 against) than on the more likely one (14, or 41 on).
See also
odds in German: Odds
odds in Italian: Odds
odds in Dutch: Odds
odds in Japanese: オッズ
odds in Norwegian: Odds
odds in Portuguese: Chance
odds in Swedish: Odds
Synonyms, Antonyms and Related Words
advantage, agreement to
disagree, allowance,
aptitude, asymmetry, at daggers drawn,
at loggerheads, at odds, at variance, bulge, chance, chances, clashing, coign of vantage,
conflicting,
contrariety,
contrast,
crosspurposes, deadwood, debris, departure, deviation, difference, difference of
opinion, differing,
difficulty, disaccord, disaccordance, disagreeing, disagreement, disconformity, discongruity, discordance, discrepancy, discreteness, disequilibrium, disparity, disproportion, dissent, dissimilarity, dissonance, distinction, distinctness, divergence, divergency, diversity, dividedness, division, draw, drop, edge, equivalent odds, even break,
even chance, expectation, fair
expectation, fair shake, far cry, favorable prospect, fiftyfifty,
flying start, fragments, good chance, half a
chance, handicap, head
start, heterogeneity,
hundredtoone shot, imbalance, in disagreement, in
opposition, inaccordance, inadequacy, incompatibility,
incongruity,
inconsistency,
inconsonance,
inequality, inequity, inharmonious, inharmoniousness,
inharmony, injustice, inside track,
insufficiency,
irreconcilability,
irregularity,
jump, lead, leavings, leftovers, liability, likelihood, likeliness, litter, long odds, long shot,
misunderstanding,
mixture, no chance,
nonconformity,
nonuniformity,
oddments, odds and
ends, opposition,
otherness, out of
line, outlook, overbalance, particles, polarization, presumption, presumptive
evidence, price, probabilism, probability, prospect, reasonable ground,
reasonable hope, rubbish, running start, scraps, separateness, short odds,
shortcoming,
shreds, small chance,
something extra, something in reserve, square odds, standoff, start, superiority, tendency, toss, tossup, touch and go,
unbalance, unconformity, unevenness, unfair
discrimination, unlikeness, unorthodoxy, upper hand,
vantage, vantage ground,
vantage point, variance, variation, variegation, variety, verisimilitude,
wellgrounded hope, whip hand