My aim was to present a new metric that would measure the effectiveness of special lineups in way that removed a lot of the noise and was easier to interpret in the context of the rest of the game.
GDA-PK represents the average goals gained or lost per hour when killing a penalty. In Table 1 below, for example, the Vancouver Canucks, have a GDA-PK this season of -3.87, so they fall behind by 3.87 goals for every 60 minutes in a 4-on-5 situation. This can also be written that the 'nucks lose a goal for every 60/3.87 = 15.5 minutes of penalty killing.
Likewise, GDA-PP represents the average goals gained or lost per hour of powerplay. Table 1 shows that the Detroit Red Wings manage to gain 8.00 goals for every 60 minutes of powerplay, or get ahead by 1 goal for every 7.5 minutes spent on the powerplay. This isn't the same as gaining 1 goal for every 7.5 minutes of penalty in favour of the Red Wings, because a lot of those penalties will be cut short by conversions.
Also note that it's 'Goal Difference', not goals scored/allowed. This way, both measures account for shorthanded goals by treating them as negative powerplay goals.
I wanted to see if there would be any major divergences between GDA measures and the traditional PP% and PK% (PowerPlay percent and Penalty Kill %) measures in terms of ranking the teams. Ideally, both measures would agree in rankings because they are intended to measure the same thing.
Notable performances are highlighted in Table 1. The Carolina Hurricanes seem to get a lot more mileage out of their powerplays than their opponents (5.66 goals/hr gained vs. 3.26 goals/hr lost). Philadelphia and Washington are very exciting to watch during penalties in both directions.
After 60 games, each team has had 5-6 hours of powerplay time, and 5-6 hours of penalty kill time. As such, there's still a lot of uncertainty in the GDA-PK and PP of individual teams. Each team value should be considered to have a 'plus-or-minus 2 goals/hr' next to it. For example, Boston's GDA-PP of 5.00 could really mean they've been gaining 3 goals/hr on the powerplay and getting some lucky bounces, or that they should be gaining 7 goals/hr, but can't catch a break this season.
We could also find the average length of a minor or major penalty, so we can use this to estimate how many goals a given penalty is worth, either league wide or for a given team. We can also find the success rate of penalty shots, assuming we can use the shootout to increase our sample size, so we could also find out how many penalty minutes a penalty shot is worth.
Another note is that even though Montreal is currently the top of the Eastern Conference standings, they're only putting up half a goal more than their opponents on the 5-on-5 or the 4-on-4. They're on par with the L.A. Kings, who are currently on the playoff bubble.
Since teams spend the large majority of their time at even-strength, GDA-EV has a lot of data to draw from. You should consider them to be (plus-or-minus 0.5 goals/hr).
In this previous post, I gave a short demo of the nhlscrapr package, which allows anybody to download a play-by-play table of every hit, shot, faceoff, line change, penalty, and goal recorded. The data used to make Tables 1 and 2 come from nhlscrapr. Select details are found in the methodology below.
Finally, only regulation play (the first 60 minutes of each game) is considered. This is to filter out any confounding issues such as teams scoring less often in overtime than they do in regulation.