Adjusted Plus-Minus (originals)

[Marvin]

Adjusted Plus-Minus

Originally Created: Late 1970's

Original Creators: Lou Nanne, Emile Francis, and others

Inspiration: Try to get players on good teams and bad to be measured on the same relative two-way scale.

Logic: How do we determine players on bad teams who are actually performing well, but are dragged down by lousy team-mates?  Conversely, who on good teams is actually performing poorly because his team-mates inflate his raw numbers?

How to compute it: There were actually 3 versions of this stat.

1. Original
   1. Background:
      1. Easiest
      2. Used by Emile Francis and Lou Nanne to help evaluate player assignments, roles, etc.
      3. Allegedly pioneered in the 1950's (!) by Anatoli Tarasov, Arkady Chemyshev, Vsevolod Bobrov, Boris Kulagin, and Viktor Tikhonov -- even before the NHL adopted +/-.
   2. Computation
      1. Add up the raw +/- stats for a given team.  Call that PM_total
      2. Divide PM_total by the number of skaters required to dress for a game.  Call that PM_ave
         1. In the 1970's, when this was developed, that number was 16.  Now, it is 18.
      3. For each player on the team who have played a "statistically significant" number of games, take his raw +/- and subtract the PM_ave.  That is his original adjusted +/-
         1. Depending on whom you ask, this could be anywhere from 30 to 60.
         2. I personally say "half a season".
2. First Revision
   1. Background:
      1. Some extra complexity
      2. Appeared in The Hockey News about 1980; introduced by Jeff Z. Klein and Karl-Eric Reif
      3. Was apparently used as far back as 1973 by Fred Shero and Joe Crozier
   2. Computation
      1. Each time a goal is scored on the ice, if the situation is one where you count a plus or minus, take the reciprocal of the number of players on the ice and multiply it by +1 (GF) or -1 (GA).  This is PM_per_player for each player on the ice.
         1. Normal Simplification: Just assume 5 players on the ice, which is typical.
         2. Note that without this simplification, goals in 3-on-3 OT are over-valued somewhat.
      2. Add PM_per_player over the entire season for the entire team.  This is the PM_ave.
      3. Also, for each goal where plus-minus applies, add the PM_per_player for each applicable player's adjusted plus-minus.  This is PM_player_raw.
      4. For each player, subtract the PM_ave from PM_player_raw.  This is his adjusted plus-minus.
3. Second Revision
   1. Background:
      1. Add more situational understanding
      2. Pioneered by Viktor Tikhonov.
   2. Computation:
      1. Use any of those above.
   3. Adjustments:
      1. Do not include empty net goals.
         1. At the time, ENG outnumbered goals scored by the team that pulled the goaltender something like 30-1, so it inflated plus figures for defencive forwards and deflated plus figures for scoring players.
      2. Weight complete gaffes against specific players who screwed up, such as a defenceman coughing the puck up to an opposing forward in the slot and "crucial goals".

Advantages: Fairly easy to derive from the raw data at the end of the year; easy to see when a player has played enough games to warrant this extra scrutiny; allows for underrated players to shine (e.g., Bill Hajt) and finds over-rated players relative to their peers (e.g., Ramsay-Luce-Gare were a better checking line than anything involving Bob Gainey!).

Disadvantages: Still kind of crude; does not do as good a job finding good players on bad teams as it should (e.g., Ron Stackhouse); allows really good players to buoy the statistics of team-mates (e.g., Dallas Smith had the good fortune to be partnered with Bobby Orr and then Brad Park).