Strength of schedule and adjusted ratings explained
Why raw records can mislead, what strength of schedule measures, how adjusted ratings correct for opponent quality, and why they give a fairer comparison.
The idea in one sentence
Strength of schedule and adjusted ratings exist to answer a simple problem: not every team plays the same opponents, so raw records and stats are not directly comparable. Strength of schedule measures how tough a team's opponents have been, and adjusted ratings correct a team's performance for the quality of the teams it has faced. Together they try to show how good a team really is, rather than how good its results happen to look.
Why raw records mislead
A team with an impressive record may have built it against weak opposition, while a team with a worse record may have played a brutal run of strong opponents. Comparing them on results alone is unfair, because the difficulty of their schedules is different. Early in a season especially, before every team has faced a balanced mix of opponents, raw numbers can flatter some teams and unfairly punish others, hiding their true level.
Adjusting for opponents
Adjusted ratings fix this by factoring in who a team has played. Instead of just counting points scored and allowed, they weigh those results against the strength of each opponent, so beating a strong team counts for more than beating a weak one. Some adjustments also account for whether games were at home or away. The result is a rating that estimates a team's quality on a level playing field, independent of the luck of its fixture list.
Why it gives a fairer picture
By stripping out the advantage or disadvantage of an easy or hard schedule, adjusted ratings let teams be compared more fairly and often predict future results better than raw records do. A team that looks average but has faced a punishing schedule may be stronger than its record suggests, while a team padding its numbers against weak opponents may be due a fall. The adjustment reveals the quality underneath the raw results.
How to read it sensibly
Adjusted ratings are powerful but not perfect. They depend on correctly rating the opponents themselves, which is difficult early on when there is little data, and they cannot capture everything, such as injuries or a team improving over time. They are best treated as a strong estimate rather than a final answer, and read alongside the raw record and the eye test to build a complete view of how good a team is.