I am asked with great frequency what it is that I have learned looking at hockey through the lens of a spreadsheet. The first part of the answer is that I have identified five important laws of hockeynomics that should shape any investigation. Failure to respect these laws will doom an analysis.
Law #1: Winning is what matters
It may seem self-evident that winning is all that matters, but a surprising number of analyses are not grounded in this law.
When measuring something, one should know the relationship of that something to winning in order to assess its usefulness. An example of statistical futility is faceoff winning percentages. These correlate very poorly with winning and are a statistic of low utility.
Some feel that winning in the playoffs is what really matters, that regular season victories don't matter much. For those people I offer up this — with 30 teams in the NHL the planets must be exceptionally well aligned for any given team to win the Stanley Cup and, in any case, the single best predictor of playoff success is regular-season success. The current Stanley Cup favourite has to be the Red Wings.
Law #2: Goals for and against are the only factors that affect winning
In any sporting event, one wins by having more credits than debits. The accounting system of some sport is complex. In hockey it is not. Hockey teams win by scoring more goals than they allow.
In a single game it is an absolute truth that the team that scores the most goals is the winner. However, over the course of a season a team with a positive average goal differential only has a tendency to win more than it loses (a consequence of Law #3).
Nevertheless the predictive power of goals for (GF) and goals against (GA) is very strong. Regression analysis tells us that about 94 per cent of winning is explained by a sophisticated model involving just GF and GA. The remaining 6 per cent seems to just be statistical noise — all other variables seem to simply drive GF or GA.
Taken together, Laws #1 and #2 tell us that 'goals are what matters'. Given that there are about six times as many goals as wins, there is much richer statistical information in the study of goals scored and allowed.
Law #3: Goals are random events
It may seem that focusing on goals violates Law #1. If a team wins a lot of games in spite of a small average goal differential, we seem to be getting mixed signals. But this is where Laws #3 comes in.
The game of hockey is played by humans at high speed in tight quarters on a slippery, but imperfect, surface with a disk made of rubber. If this does not sound like a recipe for chaotic events, watch a hockey game.
There is a great deal of statistical proof that goals occur randomly. This does not mean that skill, strategy and execution give way to luck. It means that outcomes are uncertain, influenced by a myriad of factors including skill, strategy and execution.
In fact, that is why the games are played. If variations in individual performance and conditions ('randomness') did not exist, the game would have no interest.
Most people struggle to accept this. They don't want to believe that the home team's 3-2 upset over the league leaders was a consequence of a couple of good bounces. The preference is to believe that the win came from good execution.
Humans believe in cause and effect. Yet there are too many chaotic factors in play. Randomness is everywhere in the game of hockey.
Looking lucky these days — New Jersey, St. Louis and Minnesota. These teams do not have the GF/GA records to support their winning percentages.
Law #4: Winning has a nearly linear relationship to goal differential
