In the last couple weeks I’ve seen the re-emergence of the use of +/- in discussions around the sub. While +/- isn’t the worst stat to use in the world, I thought I’d offer an explanation as to why it should be, and frankly is, being used less and less every day in hockey discussions. As well, I figured I’d provide a small explanation of alternatives that are being used for everything from possession to the difficulty of saves made during a game. “But Shweet, you idiot, we know advanced stats and how they are applied to the modern game”. You're right, this is as much for me as anything else (I want to make sure I'm not messing everything up), but at least this way there’s a list of sites that can be useful in arguments with people who may not know stats as well, or are completely misinterpreting them (I may be included in that group). Some are very well known, others are less so, but all are fairly useful, although sometimes for specific things.
First off, why is +/- not a great stat to use? Too many variables is the primary reason. +/- is very dependent on the play of all those on the ice, not just the single player who's stat you may be using to compare their play to another's. “But shweet, wouldn’t it be good then”. Not really. Why? Because it also ignores a whole lot of the contextual data that changes the picture quite a bit. +/- ignores zone starts, time on ice, matchups, etc.
If a player steps on the ice and his team gets scored on, even if he’s not involved in the play, he gets a -1. A player can have absolutely no impact on a play, positive or negative, but they gain or suffer because of a goal for or against. It can also be heavily impacted by the game you play. If we look at the Wagon line from this past season, Gordon had a -5, Hendricks had a -14 and Klinkhammer had a -7. That’s on a line where all the players played together for most of the season (or at least Gordon and Hendricks did). What about the top scoring players on the team? Ebs, despite leading the team with 63 points, was -16, Nuge, the best two way player on the team, had a -12 and Benoit Pouliot? A -1.
There’s no real consistency for point production, role and +/-, and using it to compare players becomes rather pointless. +/- variation can depend heavily on the players’ role on the team, the minutes they play, the system the coach plays, the quality of goaltending on the team, the quality of linemates, even just the luck factor of stepping out onto the ice or getting off on a line change in time. Not only that, but +/- is not at all affected by odd man play, so any goal shorthanded or on the powerplay has no affect on your +/-. You could be a powerplay specialist and put up fantastic numbers but still have a terrible +/- score. +/- doesn’t give a good indication of a players’ contributions to the team as it evaluates every player on the ice simultaneously rather than singling out a player you want to compare. Can you use it to compare year by year for a team as a whole? Certainly. But then why not compare overall goals per game, goals in different periods and situations, against stronger or weaker teams, and stats of that nature?
The biggest issue with +/- isn’t necessarily its inability to account for a wide variety of factors, but rather because there are a great deal more effective statistics that we can use in arguments. We’ve all heard Corsi, Fendwick, PDO, HERO, Adjusted sv%, oz%, iCorsi/60, etc. But what do they mean, and where can you find them? Here’s a short list:
Corsi: Corsi is the big one you likely heard a lot about lately. Corsi, along with Fenwick, are used as possession metrics, that is to say as statistics of how well a player, or team, is possessing the puck. It does so by measuring (shots on goal + shots blocked + shots missed) – (shots on goal against + shots blocked by teammates or the player + shots against missed).
Fenwick: Same thing as Corsi, but eliminates shots blocked, so it’s just (shots + shots missed) – (shots against + shots against missed).
Corsi and Fenwick for %: Gives us a ratio of corsi or fenwick for vs. corsi or fenwick against. The formula goes (100 x FF) / (FF+ FA). The same formula is used, but replaced with CF/CA when using Corsi. Used more often, if possible, than straight up Corsi for comparing players.
PDO: PDO is a stat that attempts to compensate for, due to a lack of a better word, luck. An average PDO should be 1.000. In theory, PDO’s will increase or decrease to around that point. Teams are unlikely to maintain a PDO above 1.000, or below 1.000 for extended periods of time. Formula is quite simply sv%+sh%.
Adjusted sv%: Adjusted sv% is a bit finicky. I don’t personally know a whole lot about it. Basically what it does is attempts to compensate a goaltender’s sv% to accurately depict the difficulty of the shots they are facing. In trying to find information about it though, I found two different sources, both of which calculated the statistic a little different. Here's the one from broadstreet hockey, and the one from Canucks Army. Both use slightly different methods. I'm a little more partial to the Canucks Army version as it does take into account the different shot distances and, in theory, more range of difficulties, but both have their strengths and weaknesses.
Edit: Here's a Travis Yost piece from TSN about Adjusted sv% as well.
HERO: The Horizontal Evaluative Rankings Optic gives a visualization to compare defenseman performance, attempting to show shot suppression and defensive effectiveness, and then comparing it to their peers. It uses Points/60mintues played, Corsi For/60 minutes, and GF/60 minutes (with the variations of each stat).
oz%: Ratio of offensive zone starts. Higher the number, the more offensive zone starts a player gets. Gives an indication of the difficult of minutes the player may get. While oz% by itself isn't an indicator, typically players with higher oz% are more offensively driven (especially when comparing defenceman oz%).
This post, as much as anything, is to simply compile a list of the best sites that can be used for advanced stats and contracts. The ones listed are the ones that I’ve been using primarily over the last few months, but I have more than likely forgotten or am completely oblivious to a great deal of other fantastic sites, so by all means please add to the list!
Possession and General statistics
Hockeydb: Database for hockey, as the name states. Has everything from player stats to attendance records, best players by #s, draft picks, etc.
NHL.com: Contains both stats and enhanced stats. While great for possession metrics, the NHL site is limited in advanced stats to primarily just Corsi and Fenwick (although named SAT and USAT).
Hockey-Reference.com: Has typical, primarily non-advanced stats, but does have sh%. Effective for comparing production in seasons, months or even calendar years with their splits. Splits are also used on NHL.com, however I found them easier to use on this site.
Hockey stats.ca: Useful for single game stats analysis and AHL stats.
Puck on Net: Probably the best site for pure Corsi and Fenwick comparison by team. Can compare between dates (effective for viewing the Corsi/Fenwick changes between Eakins and Nelson), and the varying Corsi when a team us tied, up 1 or 2, or down 1 or 2.
Behind the net: Another good possession metrics site. Also contains shooting metrics and goalie stats.
Hockey-graphs.com: Visualization of possession.
War-on-ice: Probably the best all around site thus far. Can compare nearly any stat you can think of in a tabular or graphical view. Can compare teams, players by position, linemates, etc. Very useful site.
Edit: Does have adjusted sv% metric function as well. What formula they use is uncertain at the moment though.
Contracts, Trades and Salary Caps
Sportrac: Useful for contracts of major North American sports. Includes information about NTCs/NMCs, past contracts, expiry dates and whether the player will be an RFA of UFA at the end of their contract.
General Fanager: Many are calling it the spiritual replacement to capgeek. I unfortunately didn't get a chance to really use capgeek to its fullest extent, so I'm not sure how accurate that is.
Hockey's Cap: Another good contract/cap structure site.
Pro Sports Transactions: Has trades made in Baseball, Basketball, Football and Hockey. Probably the best sites for trades I've found thus far.
If you made it to the end...thanks! I honestly didn't think this post would get this long. Please let me know if I've stated information incorrectly or think I should add anything for context in here. I know it's a massive wall of text, and for that I apologize. While /u/speedonthis loves his lists, I unfortunately end up going for the less than appealing "wall o' text" format more often than not. I blame my history profs. I'd also like to thank /u/arunatic5 and /u/paul-mccartney for making sure I didn't make myself look like a total idiot while writing this...I hope.