Every serious ranking system trades responsiveness for stability. Understanding which side of that trade a system sits on explains most disagreements about its output.
Averaging is what produces stability
A ranking that reacted fully to the most recent result would move constantly, and a single upset would reorder the table. Averaging across many matches suppresses that noise.
The suppression is indiscriminate. It removes random variation and genuine change equally, because the system cannot distinguish between the two as they occur.
A club improving steadily therefore appears underrated for as long as the window contains its weaker past, which can be several seasons.
Sample size is the underlying constraint
Distinguishing real improvement from a good run requires enough matches for the difference to be statistically visible, and football provides few matches per season.
Continental competition supplies even fewer, sometimes only a handful of meaningful fixtures against comparable opposition in a whole campaign.
With so little data, any system must either extend its window or accept large errors, and most choose the window.
Rating systems handle this differently from coefficients
Elo-style ratings update after every match, adjusting by an amount that depends on the result and the difference in ratings between the teams.
Because each update is small, the rating still moves gradually, but it moves continuously rather than in seasonal steps, and it incorporates the strength of the opponent directly.
Coefficient systems ignore opponent quality almost entirely, treating a win over a weak side identically to a win over a strong one, which is a substantial loss of information.
Margin of victory is deliberately excluded from some systems
Including goal difference improves predictive accuracy, because a heavy win carries more evidence about relative strength than a narrow one.
It also creates an incentive to run up scores in matches already decided, and it distorts ratings when a team plays with a numerical advantage after a dismissal.
Systems that include margin usually cap its influence, so that beyond a certain difference additional goals add little.
Squad turnover breaks the assumption entirely
Ratings assume the team being rated is roughly the same team that produced the past results. A club that has replaced several key players has broken that assumption.
No public ranking adjusts for personnel directly, which is why ratings are least reliable immediately after a transfer window or a change of manager.
Predictive models used privately do incorporate squad composition, which is the main reason their forecasts diverge from published tables at exactly those moments.
