Frequently Asked Questions

  • 1. HOW DOES THE POINT SPREAD WORK?

    Picking a straight-up (SU) winner is easy; all you have to do is select which team has the highest score at the end. That's why the point spread, also known as "the line", exists. Let's look at an example:

    Browns at Seahawks (-13.5).

    That reads "Seahawks favored by 13.5 over the Browns." It's easy to pick a straight-up winner in this game. If these two teams played each other, the Seahawks would win 9 out of 10 times. Picking the game against-the-spread (ATS), however, means you have to predict whether or not the Seahawks will win by more than 13.5 points. Let's look at some possible outcomes:

    If you pick the Seahawks at -13.5, and they win by 17, you win.
    If you pick the Seahawks at -13.5, and they win by 10, you lose.
    If you pick the Seahawks at -13.5, and they lose, you lose.

    If you pick the Browns, you're getting 13.5 points along with that bet, so the Browns plus 13.5. If you take the Seahawks, you're giving up 13.5 points, so minus 13.5.

    Notice the half point, also known as "the hook", on the point spread? The oddsmaker will typically add a half point on the line to avoid any chance of a push. That half point on the line matters, let's take a look at an example:

    If the line is -13.5 and the Seahawks win by 13, you lose.
    If the line is -13 and the Seahawks win by 13, you tie (also known as a "push").

    If you like two or more teams to cover, you can bet them separately or parlay them. In a parlay, payouts are much higher. However, if you lose one game in a parlay, you lose the entire bet. If one of those teams in the parlay pushes the payout gets knocked down accordingly; a 3-teamer parlay becomes a 2-teamer.The odds on a typical parlay are generally something like:

    2 teams 13-5
    3 teams 6-1
    4 teams 10-1
    5 teams 25-1
    6 teams 40-1
    7 teams 75-1
    8 teams 150-1

    What this means is that a bettor making a wager on a five-team parlay stands to win $25 for every $1 if all of the games win. This is why parlays are popular with sports bettors. Beware though the odds of the payoff are much less than the true odds. Also, you're not limited to point spreads when betting parlays, part of your parlay bet can include the over/under for a game.

    A teaser bet like a parlay wager where you pick two or more teams against the spread. However the key difference is that when you tease a game it allows you to move the point spread by N amount of points depending on the type of teaser you play. Just like a parlay, if one game fails to cover the spread, your bet is a loser. Payouts are typically less than a parlay for this kind of wager.

    The standard teaser is a two team six pointer with odds of -110. Odds vary from sportsbook to sportsbook however this is the norm for a two team six pointer. Let's take a look at an example of two games with regular point spreads and then the end result after we apply a six point tease:

    Dallas Cowboys (+6)
    Washington Redskins (-6)

    Chicago Bears (+10)
    Green Bay Packers (-10)

    Let's say you wanted to bet on the Redskins and Packers. You would knock 6 points off each creating a spread of Redskins at an even point spread, also known as "pick-em", and the Packers -4. You're not limited to doing this with favorites though. You could make underdog Cowboys +12, the Redskins pick-em, the Bears +16 or the Packers -4. It's your choice!
  • 2. HOW DOES THE OVER/UNDER WORK?

    The over/under, also known as "the total", is simply betting on the combined number of points both teams will score. Let's look at that Browns-Seahawks game again. If you see something like:

    Browns (46.5) at Seahawks (-13.5).

    The -13.5 is the spread, and the 46.5 is the total. You can pick the Over or the Under. If you take the Over and both teams combine for 47 or more points, you win. If instead they total 46 or less points, you lose.
  • 3. WHAT IS VIGORISH?

    All sportsbooks charge a commission known as vigorish, or simply "the vig", also known as "juice" or "the take". The vigorish is typically 5%-10% of the winning bet. Many bettors are under the fallacy that losers pay vigorish. The fact is losing bettors actually play for free because vigorish is deducted from winnings, not added to losses. This is also the way it works in many other casino games, such as craps, baccarrat, blackjack, and slot machines.

    To illustrate this imagine two bettors each risk $110 with the same bookmaker on opposite sides of the same proposition, each bettor trying to win $100: The bookmaker receives a total of $220 from the two bettors. One bettor wins, one bettor loses, and the winner picks up a total of $210; the $110 he put at risk, plus his $100 profit. That leaves the bookmaker with $10 gross profit as his vigorish on the deal. The bookmaker kept $10 of the $220 total amount risked, and it was the winner who paid it.

    The vig matters because if there was no vigorish all you would have to do to make money is pick at 50.1 percent, which is essentially flipping a coin. With the vig, however, you have to pick close to 52.5 percent, which is much more challenging. To illustrate this, imagine if you made 100 $1 bets and won 53 of them. You would win $53 and lose $47. So you're up $6. But on top of the $47, you lose another $5.30 (the 10% vig) and net only $.70.
  • 4. HOW DO YOU CALCULATE RPI?

    The Ratings Percentage Index (RPI) is measure a team's strength of schedule and how a team performs against that schedule. This index considers whether a team won or lost but not the margin of the victory. More weight is given to teams playing and winning games on the road. Teams with a high RPI are more successful. It is calculated using the following formula:

    Ratings Percentage Index (RPI) = (WP * 0.25) + (OWP * 0.50) + (OOWP * 0.25)

    Where:

    WP = Winning Percentage OWP = Opponents' Winning Percentage OOWP = Opponents' Opponents' Winning Percentage

    and

    The WP is calculated by taking a team's wins divided by the number of games it has played (i.e. wins plus losses).
  • 5. WHAT DOES THE MARGIN COLUMN REPRESENT?

    The Margin column shows the ATS Margin for a team in a single game. This is the number of points between the point spread and the margin of victory. For example, if the Seahawks were 10-point favorites over the Browns and ended up winning by 20, then the ATS Margin would be 10. If the Seahawks had won by 5 points, on the other hand, the ATS margin would be -5. On the Rankings page we show the average ATS Margin in the Avg Margin column. Margin and Avg Margin are calculated using the following formulas:

    Margin (MAR) = Margin of Victory - Point Spread
    Avg Margin = Total MAR / Number of Games Played

    The results are color coded to judge the severity of the final result versus the spread.
  • 6. HOW DO YOU CALCULATE PRD?

    Passer Rating Differential is obtained by subtracting a team's Defensive Passer Rating from its Offensive Passer Rating. This statistic has proven to have a direct correlation to SU victory. Teams with a high Passer Rating Differential are successful. Teams with a low Passer Rating Differential are not successful. It is calculated using the following formula:
    Passer Rating Differential (PRD) = Team Offensive PR - Team Defensive PR

    Passer Rating (PR) = ( (mm(A) + mm(B) + mm(C) + mm(D) ) / 6) * 100

    Where:

    A = ((Comp / Att) - .3) * 5
    B = ((Yds / Att) - 3) * 2.5
    C = (TD / Att) * 25
    D = 2.375 - (Int / Att * 25)

    and

    mm(x) = Max(0,Min(x,2.375))

    The maximum possible quarterback rating for the NFL 158.3. A perfect rating requires at least a 77.5% completion rate, at least 12.5 yards per attempt, a touchdown on at least 11.875% of attempts, and no interceptions.
  • 7. HOW DO YOU CALCULATE YPPA AND YPPS?

    Yards Per Point Allowed (YPPA) is a team-wide measurement of ability to keep opponents off the scoreboard, their bendability. It takes into account a variety of factors (including proficiency of offense and special teams, red zone defense, and turnover differential). A team's bendability is obtained by calculating:

    Yards Per Point Allowed (YPPA) = Yards Allowed/Total Points Allowed

    The higher the number, the more difficult a team makes it for opponents to score points.

    Yards Per Point Scored (YPPS) is a team-wide measurement of ability to turn yards into points, their scoreability. It takes into account a variety of factors (including proficiency of defense and special teams, red zone offense, and turnover differential). Other measures of offense, and offensive efficiency, look at the offensive unit in a vacuum, we don't. A team's scoreability is obtained by calculating:

    Yards Per Point Scored (YPPS) = Offensive Yards/Total Points Scored

    The lower the number, the more efficiently a team scores points.
  • 8. HOW DO YOU CALCULATE PASS YARDS PER ATTEMPT?

    Yards per pass attempt (Yds/Att)is a stat that has a direct correlation to SU wins. We use only net passing figures to determine yards per attempt. This is gross passing yards, minus yards lost via sacks, divided by passsing attempts. In addition to dividing the net passing yardage by pass attempts, we also add in the number of sacks to the attempts column. We believe this gives a far more accurate gauge of a team's ability to pass the ball. A team's ability to pass is obtained by calculating:

    Yards per pass attempt (Yds/Att) = (Passing Yards - Sack Yards) / (Pass Attempts + Sacks Allowed)

    This is different than what you will see on other websites but we believe it's better. After all, when a QB is sacked, it's because he was attempting to pass. For example, if a quarterback attempts 10 passes for 100 yards, his yards per attempt is 10.0. However if that QB was sacked three times and lost 22 yards then the team's passing yards per attempt is a only 6.0 (78/13). The team gained 78 net yards when attempting to pass and those three sacks came on attempts to pass.
  • 9. HOW DO YOU CALCULATE REL?

    Relativity Index (REL) measures the performance of A team relative to the performance of its opponents in all other games. Like the RPI ranking, the Relativity Index can tell you about the quality of each team's competition and how greatly a team overachieved, or how badly a team underachieved, relative to the quality of their competition.

    Relativity Index (REL) = TPS-OTPA + OTPS-TPA

    Where:

    TPS = Total points scored, on average, by the team
    OTPA = Opponents' points allowed, on average, in all other games
    TPA = Points allowed, on average, by the team
    OTPS = Opponents' points scored, on average, in all other games

    If the Seahawks scores 30 Points Per Game (PPG), and their opponents give up 10 PPG in all of their other games, then the Seahawks are +20.0 PPG on offense. If the Seahawks give up 10 PPG, and their opponents score 25 PPG in all of their other contests, then the Seahawks are +15.0 on defense. This means the Seahawks have a Relativity Index of +35.0 PPG, which means they are 10 points better than the average performance of its opponents.
  • 10. HOW DOES YOUR DATA API WORK?

    We offer programmer access to the raw data that we use for our trends through an Application Programming Interface (API). Our flexible API can be used to create your own interesting applications based on the latest NFL game data. For a complete list of the different operations that are available please refer to our API Documentation page.

    You can purchase an API access key from our Season Pass page. After purchasing API Access you will be emailed a key that can be used on data requests. The key must be appended to each web request by adding the querystring parameter ApiKey=[YOUR_API_KEY_HERE]. For example, to query a list of all games played in the 2012-2013 season you would make the following web request:

    http://www.spreadtrends.com/api/nfl/games/2012?ApiKey=[YOUR_API_KEY_HERE]

    If you do not have a valid API Key on your request you will be redirected to the login page.

    All NFL game stats are updated by Tuesday at 6pm EDT.