VOA – A different approach to NRL statistics
Two teams both play on a weekend. Both teams register 3 line breaks. Who performed better? According to conventional NRL statistics, they performed equally well. But what if Team A was playing the Melbourne Storm, and let’s say the Storm concede an average of 1.5 line breaks per game. And let’s say Team B was playing against the Wests Tigers, and hypothetically they concede an average of 6 line breaks per game. Now who played better? Surely the team who achieved their 3 line breaks against the notoriously stingy Storm defense performed better than the team who could only achieve 3 against the typically leaky Tigers defense? And there, within that simple example, is the inherent problem with conventional NRL stats, and the basic idea behind VOA-based NRL statistics (Value Over Average).
Context is everything
Statistics are everywhere now in rugby league. We’re acclimatized to seeing statistics on our television sets, in our newspapers, and on the websites we frequent. However, these NRL stats are simply a recording of events – a number of metres, a number of line breaks, a number of tackle breaks and so forth. The records fail to account for the most important part of any event – context.
Which opponent were they playing? Is that opponent above average or below average? How much possession did they have? Without accounting for the context in which an event occurred, the statistic itself holds little value.
Most would agree that if two teams achieve an identical result, the result against the higher quality opponent should be worth more. But how much more? VOA-based NRL statistics attempt to solve this problem.
Let’s take our original example. Our imaginary Melbourne Storm defense concedes an average of 1.5 line breaks per game. Team A have managed to put 3 line breaks past this defense. The VALUE OVER AVERAGE in this example would be 100% (3 is 1.5 more than 1.5, which is obviously 100% of 1.5). Team B, however, posted their 3 line breaks against the Tigers, who in our example concede an average of 6 line breaks per game. So, their VALUE OVER AVERAGE is -50% (3 is 3 less than 6, and 3 is 50% of 6). So, where conventional statistics would have simply credited both teams with 3 line breaks, we have now established that Team A scored a LB VOA of 100%, while Team B scored a LB VOA of -50%. What this example illustrates is that while conventional NRL statistics only tell us what happened, VOA-based NRL statistics also assess that performance.
The value over average of Value Over Average
We typically measure the performance of teams and players by their statistics, whether those be their season totals or their per game averages. However, the NRL draw is inherently unfair – teams do not all play each other twice, and indeed at certain points of the competition teams could have played some opponents twice while still not having played others at all. Because of this, using conventional NRL stats to measure performance will present a skewed data set depending on the quality of each team’s opponents, and hence produce an inaccurate measurement. VOA-based statistics, however, attempt to level that playing field by accounting for such variables.
Another advantage of VOA-based NRL statistics is that by representing the statistics as a percentage over average rather than a dry number, the statistic itself is provided with context. Let’s say that a team averages 3 line breaks per game. Is that good or bad? Without other teams’ averages to provide context we have no idea. However let’s say instead that a team averages a LB VOA of -25%. We now have a clear picture of this team’s ability to create line breaks (or lack thereof).
Also, by representing the data as a percentage over average, VOA-based statistics provide a fairer method of comparing teams from different years, or even different eras. A team who averages 4 line breaks a game may be below average in 2016, however in 1986 that may have been exceptionally good. By using VOA, we are able to see at a glance how well a team performed relative to their contemporaries.
Now that we’ve established the value of VOA-based NRL statistics, let’s make sure we understand the most important part – interpreting them.
Fortunately, VOA-based statistics contain within themselves their own scale. That is, 0% is average, and every percentage increase or decrease is that amount above or below the league average. This comes with one important point to remember: Because the objective of rugby league is to score points, attacking stats are better when they are POSITIVE, however defensive stats are better when they are NEGATIVE.
This makes logical sense when you consider what each statistic represents. For example, if the league average for Run Metres Conceded is 1500 per game, and a team concedes just 1000 (33% below average, or VOA -33%), they have obviously done very well (since conceding less metres is better).
You can find the latest NRL VOA Ratings here!