Power Ratings are a computerized method of ranking based on a team's performance
against other teams in the league.
The IHSLA does not use power ratings to determine conference champions or state
champions. Starting in 2013, power ratings will be used to determine playoff seeding
There are dozens, perhaps hundreds, of power rating schemes employed in sports.
The power rating method utilized on this site is similar to the "Margin of
Victory" method used by LaxPower.com. The MOV method considers only the goal
differences between teams. It does not consider win/loss records nor does it
consider head-to-head contests. The IHSLA power rating scheme differs from the
LaxPower rating scheme in that it only considers play within the IHSLA and
ignores games played outside of Illinois. The IHSLA method employs two
"adjustments" to the standard power rating scheme.
The "10-Goal Limit" factor (TGL)
The TGL adjusts the ratings in such a way that a winning team will not gain additional
power points if they win by more than ten goals. Similarly, the defeated team will
not lose power points if they lose by more than ten goals. The IHSLA recognizes
that a ten-goal differential in a game results in many unusual situations such as
a running clock, more substitutions, etc. that may not represent the true performance
of either team. In addition, the TGL removes any incentive for a coach to "run up
the score" merely to improve the team's power rating.
The "Top Team" factor
The scores from various games are not all weighted equally. Games in which the opponent
is highly rated are weighted more heavily than games in which the opponent is rated
lower. This factor provides more power points to the teams with difficult schedules
and reduces the power points for teams with easier schedules. It rewards teams who
win against strong opponents, and it diminishes the rewards for teams who win against
Strength of Schedule (SOS)
The SOS rating (not displayed) is a reference to the strength of a team's opponents.
It is calculated from the average power rating for a team's opponents in games
played. The SOS rating does not reflect the strength of opponents for unplayed games,
exhibition games, or tournament games. The SOS Ranking (displayed) is a team's
rank relative to the other teams based on its SOS rating. The higher the SOS rating,
the lower the SOS rank. The SOS ratings and rankings are not used directly in any
other calculations because the power ratings are already weighted in favor of strong
opponents using the Top Team factor.
But what does it all mean?
The power rating system is a computerized method of predicting the difference in
scores between two teams. Theoretically, a team with a power rating of 95 is expected
to defeat a team with a power rating of 92 by three goals on a neutral field. Of
course, the actual outcome of such a game may be different depending on many circumstances,
but, on average, the power ratings tend to properly rank teams based on how they
performed against one another. The more games that are played within the league,
the more accurate the power ratings reflect the true performance of the teams and
the stronger the prediction mechanism becomes.
How accurate is it?
A study was conducted on the IHSLA data (May 19, 2009) after about two thirds of
the season's games were played. The study compared the actual game results to
the predicted goal difference between the two teams based on the power ratings.
The statistical analysis suggested the power rating prediction has a standard deviation
of about +/- 3 goals. To put it another way, roughly 70% of the games played had
actual results within 3 goals of the predicted goal difference.
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