How It All Works
If you are confused by the stats in the boxscores or in Stats Drop, here's a short reference guide to what the jargon means.
This is an abbreviated version of the full How It All Works explainer on pythagonrl.com.
Pythagorean expectation: There is a relationship between for and against and winning percentage, which is expressed by the Pythagorean expectation formula. This formula is used to estimate the number of wins a team should have based on their points scored and conceded. Generally, if a team outperforms their Pythagorean expectation (that is, wins more games than predicted by the formula) they will win fewer games than predicted by the formula in the following season, all other things being equal, and vice versa. Pythagorean expectation gets increasingly accurate at estimating win percentage over a longer time period.
SCWP: Should-a Would-a Could-a Points utilises metres gained and conceded and line breaks gained and conceded to estimate the number of points that the team should have scored and conceded. As this metric utilises repeatable statistics that are less prone to randomness to estimate team quality, it is marginally more reliable than looking at just the scoreboard and is a good measure of a team’s opportunities. The ratio of converting these opportunities to actual points (or defending them) is referred to as the team’s efficiency. When SCWP are used in a Pythagorean expectation calculation, in lieu of actual points, these are called 2nd Order Wins.
Taylor Player Ratings: Taylors (Ty) are the units for measuring production, the sum of valuable work done on the rugby league field, as measured by counting statistics that correlate with winning (e.g. tries, run metres, breaks, assists, etc). Teams that have higher production tend to win more games and teams with highly productive players tend to have higher production.
Taylors by themselves can be misleading, so we have:
TPR: Taylor Player Rating. This compares the amount of production done by the player to the average player in that position, adjusting for time spent on the field. An average player has a rating of approximately .100, with fringe first graders sitting at .060 and top players nearing .180. To qualify for TPR, a player must play at least five games in a regular season.
WARG: Wins Above Reserve Grade. This compares a player's production that to a typical fringe first grader in that position to estimate the number of additional wins the player's team gains by having him on the roster. This concept was explored in What makes a million dollar NRL player? and Rugby league’s replacement player.
The women’s equivalent to Taylors is Teitzels (Tz) and we make the distinction as the dataset for the women’s game is more limited.
Elo ratings: Elo ratings were developed by Arpad Elo to rank chess players and are now used in FIFA's official world rankings. I've been using Elo ratings since 2017 to assess the quality of rugby league teams.
The variables behind each system and league are different but typically, the average rating is 1500 and a higher rating reflects a better team. We can use the difference in Elo ratings to calculate the winning probability of two teams. I maintain two systems for each league -
Form ratings are designed to reflect short term performance and move quickly to reflect recent results. The system variables are optimised to maximise head-to-head tipping success. When two teams match up, an expected margin is estimated between the two teams based on their respective ratings. If a team beats the expected margin, and even if they lose the match, their rating goes up by exactly the same amount the other team's rating goes down. Form ratings only track regular season performance.
Class ratings are slower moving than form ratings and take multiple seasons to change significantly. Unlike form ratings, class ratings go up only when you win. They go up more for winning finals games and more still for winning grand finals. Class ratings reflect team's innate quality and act as a handbrake from looking too closely at the last couple of matches. For example, a team wrecked by Origin selections may have a poor form rating at the start of August but will maintain a high class rating.
Run and Tackle Shares over Expected (Run SoE and Tkl SoE): These are bastardised versions of the League Eye Test’s Run% and Tackle%. Each player’s runs and tackles are calculated as a share of the team’s total runs and tackles. The average share of runs and tackles made by all players in the NRL at that position is then subtracted from this number, resulting in a number that is positive for players who had a higher proportion of runs and tackles than the average player in their position and negative for those who had a lower proportion.
As the total shares of runs and tackles adds up to 100% across the team (i.e. if one player’s share is over, another’s by definition must be under), this metric is not predictive and unsuitable for non-trivial player comparisons. However, SoE can describe playing styles and highlight effort areas that Taylors cannot.