Understanding Odds

1. Understanding Odds Football
2. Understanding Odds Of Winning
3. Understanding Odds In Horse Racing

How NFL Odds, Lines, Point Spreads and Totals Work

When you wager on NFL football it’s important that you understand clearly and concisely how to read odds and how they work. This is basic information that you must know in order to make informed bets.

You’ll need to know how the rotation number, point spread, moneyline and over/under are used and what each means. Each of these terms may be called by another name. The rotation number if often referred to as the number or the rotation mark, moneyline becomes line, point spread is called the spread, and over/under becomes the total. When you come down to it, these are the major terms that can be lumped under the heading odds.

Bookmakers use odds to even out the bets, getting gamblers to wager on both sides of the line by leveling the playing field. Although there is overall parity in the NFL, there are teams that are haves and others that are have-nots. Indianapolis is still superior to Cincinnati but when they play each other the bookies have to get about half of the bettors to put cash on the Bengals. This covers the sportsbooks ensuring they’ll make a decent amount of cash on just about every game.

When you read NFL odds, you’ll first see the date and time of the game on the left and then immediately to the right, there will be two numbers with the name of each team next to one of each numbers. That number is called the rotation number.

• Understanding odds is the key to figuring out which bets are worth taking Odds are displayed in a variety of different formats, but all are easy to understand You can use odds to calculate the implied probability of a certain outcome in a sporting event.
• For beginning sports gamblers, moneylines (sometimes called money lines or American odds) can be confusing.Unlike point spreads, which are concerned with who wins and by how much, a moneyline is solely dependent upon who wins.

Rotation numbers are standard from sportsbook to sportsbook. The number becomes a way to refer to the game and team without mentioning the teams name. It’s a sort of shorthand. Also, the rotation number allows each book to list the games in the same order—numerically. It is, in essence, a way to keep all of the games that are posted each day and throughout the week organized. That makes it easy for the bettor and the bookie.

Everything starts with the concept of probability. Let’s say that the probability of success of some event is.8. Then the probability of failure is 1 –.8 =.2. The odds of success are defined as the ratio of the probability of success over the probability of failure. GhSMART is the most trusted advisor on leadership strategy, offering support across a broad range of solutions, including CEO succession, leadership selection and development, M&A diligence, and team and organizational effectiveness.

As an example, let’s consider a matchup between the Indianapolis Colts and the Cincinnati Bengals. In our scenario, the Bengals are the home team, which means they will be listed last and the Colts, as the visitors, will be on the odds slip first. If Indy’s rotation number is 101, then Cincy’s rotation mark would be 102. When you place a bet live at a Vegas sportsbook or over the phone, you would say the number of the team on which you want to wager and not the name.

To the right of the team’s name are the different types of odds. Usually the spread will be first. You may then see the moneyline (although some books list these on another slip) and then, finally, the over/under. Thus, all of the basic bets are in one place, allowing for easy access.

The point spread, which is the most popular type of bet, lists the favored team with a minus sign and a number and the underdog with a plus sign and the same number as the favorite. (If neither team is favored, they will be listed as EVEN or PICK.)

The team that has the minus sign, which is the favorite, has points deducted from its final score, while the dog, with the plus sign, has points added. The favorite must beat the spread, which means they have to win by more than the negative number to pay off. The underdog pays off in two instances—if they win outright or if they lose by less than the spread.

In our scenario, Indianapolis is at -10.5 and Cincinnati at +10.5. If you bet on the Colts at -10.5, which means they are favored, they must win by 11 or more for you to collect on your bet. If you wager on Cincinnati, which is the underdog, your bet pays off if they win the game outright or if they lose by less than 11.

Sometimes with NFL odds you’ll see a spread posted as a whole number. Decimals or fractions are usually utilized to ensure there won’t be a tie. If in our example the spread was reset to 10 with the Colts favored and they win by 10, then the game is considered to be a tie, which in betting terms is called a push. If there is a push all bets are off and the sportsbooks return all wagers back to the bettors.

Many people will say that the odds on a spread bet are even, paying 1:1. But this is not true. The actual odds are 0.90:1. For every dollar bet, you can win 90 cents. When checking out the spread, you’ll usually see a number listed next to each spread. That number, which is your stake, is posted as -110. This number tells you how much you have to bet to win $100. If you put $110 on either team, you stand to win $100. If you bet $11.00, you can win $10.00. Every NFL point spread works this way.

The moneyline is different. First, with the moneyline whichever team wins the game pays out. There’s no giving or taking away of points. How do the bookies even the playing field with the moneyline? They do it by making bettors wager more on the favorite to win less and allowing them to bet less to win more on the dog. The favorite is posted with a minus sign and a number. That number represents the amount of cash that has to be wagered in order to win $100. The underdog, on the other hand, is listed with a plus sign in front of a number. That number shows how much a bettor wins when they bet $100.

Understanding Odds Football

Taking the exact same match up and odds above, Indy would be listed at -380 and Cincy at +355. When wagering on the Colts, the favored team, a sports bettor would be required to bet $380 to make $100. If they take the Bengals, who are the underdog, a $100 bet can result in a $355 profit.

By the way, there is a relationship between the spread and the moneyline. The exact relationship can vary a bit depending on the book, but the correlation works in this manner:

When considering NFL odds, the last type of basic bet you’ll see listed is the total or over/under. The over/under is a prediction regarding the total number of points that both teams will score. As it is with the spread, the total is usually posted as a fraction or decimal and the stake is the same as it is with the point spread (-110)

With NFL odds the over/under can vary but usually it’s somewhere between 35 and 47 points. Let’s say in the Colts and Bengals game that the total is posted at 37.5. If Indy scores 27 and Cincy gets 13 points, the total would be at 40 and the over would win. But if the Colts rack up 35, and they shut out the Bengals, the total of 35 would be under.
If, as it is sometimes with the spread, the total is listed as a whole number, the result may be a push. Let’s say the total is 37 and the Colts score 24 and the Bengals 13 for a total of exactly 37 points. If this happens all bets are returned on the push.
If you are able to interpret NFL odds and know what the various terms mean, such as the rotation number, point spread, moneyline and over/under, you’ll have a basic understanding on what you are betting. Prior to wagering make sure you see our NFL odds page, which carries all the latest odds from the top online sportsbooks. Remember that the odds makers are attempting to even the out the bets on each game. The sports bettor has to analyze each game and the odds and make their bets accordingly in order to win cash.

Written by Clay Smith

Idiot’s Guide

That’s right - I will be your guide. The good thing about having an idiot for a guide is that I have to make it simple to understand it myself, which means, hopefully, you will understand it as well.

Probability or Odds

Probability
Probability means the risk of an event happening divided by the total number of people at risk of having that event. I will use the example in a recent JAMA article. In a deck of 52 cards, there are 13 spades. So, the risk (or probability) of drawing a card randomly from the deck and getting spades is 13/52 = 0.25 = 25%. The numerator is the number of spades, and the denominator is the total number of cards.

Odds
Odds seems less intuitive. It is the ratio of the probability a thing will happen over the probability it won’t. In the spades example, the probability of drawing a spade is 0.25. The probability of not drawing a spade is 1 - 0.25. So the odds is 0.25/0.75 or 1:3 (or 0.33 or 1/3 pronounced 1 to 3 odds).

Moving back and forth
To go from odds to probability, simply take the numerator/(denominator + numerator). In the spades example, the odds of 1/3 is converted by taking 1/1+3 = 0.25 - and now we are back to probability. To go from probability to odds, simply take the numerator/(denominator-numerator). In the spades example, given that the probability of drawing a spade is 1/4, take 1/(4-1) = 1:3 odds or odds = 0.33.

Statistical Significance
If an odds ratio (OR) is 1, it means there is no association between the exposure and outcome. So, if the 95% confidence interval for an OR includes 1, it means the results are not statistically significant. Example, exposure to colored vs white Christmas lights was associated with an increase in jocularity score, OR = 1.2 (95%CI 0.98-1.45). Sorry, this is not statistically significant. Let’s just go with white lights…

Use
Either the OR or risk ratio (RR) could be used in many study types. However, only the OR can be used in case-control studies. Because in order to calculate the RR, one must know the risk. Risk is a probability, a proportion of those exposed with an outcome compared to the total population exposed. This is impossible in a case-control study, in which those who already have the outcome are included without knowing the total population exposed.

Risk Ratio

RR is a very intuitive concept. It is the probability (or risk) of one outcome over the probability (risk) of another. Let’s use a study we covered on JF to discuss this concept. Survival was lower in pediatric patients intubated during arrest compared with those not intubated: 411/1135 (36%) vs 460/1135 (41%). So, the RR is 36.2%/40.5% = 0.89. This means survival was reduced by a factor of 0.89 for pediatric arrest patients who were intubated during arrest vs. those who were not. As an example, if survival was expected to be 40%, then intubating during arrest would reduce it to: 40% x 0.89 = 35.6%.

Let’s do one more example. Supination-flexion (SF) vs hyperpronation (HP) to reduce nursemaid’s elbow was more likely to fail. The risk of failure with SF was 96/351 (27%) vs. 32/350 (9%) with HP. The RR was 3. This has a very intuitive meaning: risk of failure with SF was three times more likely than HP.

Odds Ratio

The OR is a way to present the strength of association between risk factors/exposures and outcomes. If the OR is <1, odds are decreased for an outcome; OR >1 means the odds are increased for a given outcome. Let’s look at the examples again and consider odds.

For pediatric arrest, the risk of survival if intubated during arrest was 411/1135 (36%) vs 460/1135 (41%) if not intubated. Let’s convert to odds and calculate an OR.

• Intubated: 411/1135-411 = 411/724 = 0.57 odds.

• Non-intubated: 460/1135-460 = 460/675 = 0.68 odds.

• So, the OR is 0.57/0.68 = 0.83.

Note, this is very close to the RR (0.89) but is a slight overestimate of the effect on the outcome. This is always the case with the OR compared to the RR - it overestimates the effect.

Take the example of supination-flexion vs hyperpronation for nursemaid’s. The risk of failure for SF was 96/351 vs. 32/350 with HP. Let’s convert this to odds.

• SF: 96/351-96 = 0.376 odds

• HP: 32/350-32 = 0.10 odds

• The OR is 0.376/0.10 = 3.7

Note, the OR overestimates the RR, which was 3. Although one could say the risk of failure using SF is 3 times greater than HP, one could not say, based on the OR, the risk was 3.74 times greater. The OR and RR are not the same. What could be said is that the odds of failure is 3.74 times greater.

Risk Ratio vs Odds Ratio

Whereas RR can be interpreted in a straightforward way, OR can not. A RR of 3 means the risk of an outcome is increased threefold. A RR of 0.5 means the risk is cut in half. But an OR of 3 doesn’t mean the risk is threefold; rather the odds is threefold greater. Interpretation of an OR must be in terms of odds, not probability. Again, the OR will always be an overestimate compared to the RR. However, the RR and OR will be similar for rare outcomes, <10%. But the OR increasingly overestimates RR as outcomes exceed 10%. This is easier to understand with an example.

Pretend a new vape, Vapalicious, is associated with cancer.

• 80/100 people who use it get cancer.

• 20/100 who don’t use it get cancer.

• The risk of getting cancer is 4 times greater in Vapalicious users. RR = 0.8/0.2 = 4

• Note how distorted the OR becomes in this example. OR = (80/20)/(20/80) = 16

What if Vapalicious rarely caused cancer?

• 5/1000 get cancer with Vapalicious vs 2.5/1000 for non-users.

• RR = 2.

• OR = 2 as well (actually 2.005)

• With rare outcomes, the RR and OR are very similar.

Understanding Odds Of Winning

Why Does This Matter?

This matters because we often equate the OR and RR. Unwary researchers, reviewers, or news media might report a 16-fold increased risk of cancer from Vapalicious. In fact, there was a 4-fold increased risk of cancer from Vapalicous. Not that I plan to use Vapalicious (or any other vape), but a 16-fold vs 4-fold increase is a gross overestimation of the effect.

What Does the OR Mean?

So, what does an OR mean? Here it is in plain language.

• An OR of 1.2 means there is a 20% increase in the odds of an outcome with a given exposure.

• An OR of 2 means there is a 100% increase in the odds of an outcome with a given exposure. Or this could be stated that there is a doubling of the odds of the outcome. Note, this is not the same as saying a doubling of the risk.

• An OR of 0.2 means there is an 80% decrease in the odds of an outcome with a given exposure.

Summary

• Odds Ratio is a measure of the strength of association with an exposure and an outcome.

  • OR > 1 means greater odds of association with the exposure and outcome.

  • OR = 1 means there is no association between exposure and outcome.

  • OR < 1 means there is a lower odds of association between the exposure and outcome.

• If the 95% confidence interval for the OR includes 1, the results are not statistically significant.

• OR and RR are not the same.

• OR always overestimate RR, but…

• OR approximates RR when the outcome is rare but markedly overestimates it as outcome exceeds 10%.

References

Understanding Odds In Horse Racing

1. The odds ratio by Bland and Altman, of Bland-Altman plot fame

2. Wikipedia aka source of all statistical knowledge