Website Help
Frequently Asked Questions
Some common questions you may have about the calculations on our website
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1. 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). -
2. WHAT DOES THE MARGIN COLUMN REPRESENT?
The Margin column shows the number of points a team won or lost by in a single game and it includes the point spread in that calculation. For example, if the Seahawks were 10-point favorites over the Browns and ended up winning by 20, then the Margin would be 10. If the Seahawks had won by 5 points, on the other hand, the margin would be -5. On the Rankings page we show the average 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. -
3. 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, and incredible, correlation to victory and championship success, straight up. 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. -
4. 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. -
5. 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. -
6. 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. The index is obtained by calculating:
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. -
7. 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 2020-2021 season you would make the following web request:
https://www.spreadtrends.com/api/nfl/games/2020?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.