An explanation of the calculations used in this post are available at the bottom of the page.
Every possession play that occurs on the ice has both an expected goal value (EGV) and an expected shot value (ESV). The goal value is represented by the chance of that specific puck-possession play eventually producing a goal. The shot value is the chance of that specific play eventually producing a shot on net.Expected goal and shot value can be calculated by using the success-rate of that specific play, as well as the success-rates of all succeeding plays. The goal of this is to determine how successful that play has been to either produce a shot-on-net, or a goal.
When looking at the EGV's communicated here, it's important to note the similarities in values, as logic would indicate that regardless of the players involved, the average success-rates of these events should produce similar results. After all, it's the same game for both teams.
It's also important to note that over the course of their 6 game series win over the Habs, the Rangers actually produced 32 more even-strength scoring-chances than they allowed. This helps explain why the Rangers produced higher EGV's than Montreal's season and playoff totals.
I'm hoping to go deeper into comparisons in future posts.
RANGERS OFFENSIVE-ZONE EXPECTED GOAL VALUES
HABS OFFENSIVE-ZONE EXPECTED GOAL VALUES
RANGERS NEUTRAL-ZONE EXPECTED GOAL VALUES
HABS NEUTRAL-ZONE EXPECTED GOAL VALUES
RANGERS DEFENSIVE-ZONE EXPECTED GOAL VALUES
HABS DEFENSIVE-ZONE EXPECTED GOAL VALUES
Conditional Probability
For example, we know that for a pass to the slot to result in a shot, the player passing the puck to the slot has to be able to succeed with his pass. Also, the player receiving the pass has to be able to get his shot through to the net.
Using 100 attempts (to simplify the explanation), if David Desharnais is successful with 39% (tops among forwards) of his attempted passes to the slot, we know that the player receiving the pass will have 39 shot attempts as a result of those 100 passes (100*0.39=39).
If the player taking the shot is Max Pacioretty, and 6.6% of his attempted shots result in a goal, we can then calculate the expected shot value of that initial pass by calculating how many of those 38 attempted shots would result in a goal (0.066*39=2.57). This tells us that a pass to the slot from Desharnias to the Pacioretty has an expected goal value (EGV) of 2.57; as it has succeeded in the past at a rate of 2.57%.
The expected shot value could also be calculated using Desharnais pass to the slot success-rate combined with Pacioretty's success-rate getting shots through to the net. (percentage of attempted shots that hit the net). For example, Pacioretty's shots-through success-rate was 53% (0.53*39=20.67). So a pass to the slot from Desharnais to Pacioretty has an ESV of 20.67, as that play was successful in the past at a rate of 20.67%.
This system will allow us to potentially determine the goal or shot value of any play on the ice. The key is to include every potential succeeding play as well.
For the sake of simplicity, I used the average success-rates of Montreal Canadiens forwards to calculate all succeeding plays. In other words, the average success-rate of Habs forwards within each succeeding play was used in the calculation. That said, the success-rate of any combination of players can be calculated using this model. The success-rates used in this post where determined using the data from every Montreal Canadiens 2013-14 regular season and 2014 playoff game. A list of all the events I track can be found here.
