Question About Adjusted Stats

[ted2019]

I e-mailed Hockey Reference about on how They figure out the numbers for the adjusted stats. This was Their answer:
The Adjusted Stats extrapolate everything up to an 82-game schedule, his adjusted GP would be 82 times (his games / his teams' scheduled games).[/B]

My question is the following, Bobby Clarke had 89 Assists in 80 Games in 1974-75 season, but His adjusted Assists went down to 78 Assists for that season. Does anyone here know the mathematical equation They used to come up with 78 Assists?

Click to read more...

 

[Czech Your Math]

I e-mailed Hockey Reference about on how They figure out the numbers for the adjusted stats. This was Their answer:
The Adjusted Stats extrapolate everything up to an 82-game schedule, his adjusted GP would be 82 times (his games / his teams' scheduled games).[/B]

My question is the following, Bobby Clarke had 89 Assists in 80 Games in 1974-75 season, but His adjusted Assists went down to 78 Assists for that season. Does anyone here know the mathematical equation They used to come up with 78 Assists?

They also factor in the league GPG that season, although they use a more complex formula (which I tend to disagree with) than that. Since '75 was a higher than average scoring season, his adjusted production is adjusted downward accordingly.

 

[ted2019]

Do You know or can You figure out the formula that They use?

 

[Czech Your Math]

Do You know or can You figure out the formula that They use?

Hockey Reference Adjusted Stats Explanation

 

[hatterson]

http://www.hockey-reference.com/about/adjusted_stats.html describes it in detail.

They have 3 adjustments:

- Schedule. Normalize everything to 82 game seasons by dividing totals by season length and multiplying by 82.
- League scoring. For goals, normalize everything to 6 goals per game by dividing league wide goals per game *without* the player in question and multiplying by 6. For assists, normalize everything to 10 assists per game (6 goals * 1.67 assists per goal) by dividing by league wide assists per game *without* the player in question and multiplying by 10. For points, simply add adjusted goals and adjusted assists.
- Roster size. Adjust to an 18 skater roster by dividing allowed roster size in a season by 18. Theoretically this is to account for a player making up a larger percentage of his team and thus being expected to make up a larger percentage of the scoring.


Personally, I have a few issues with this approach. I don't agree with excluding the player from era averages, especially when you're dealing with massively different league sizes. In the 52-53 season they chose, Gordie Howe made up just over 3% of *all* NHL assists, but he also played in 1/3 of all NHL games that season. In a 30 team league a player plays in 1/15th of league games. In 05-06 Thornton had 96 assists in 81 games, but that made up well under .8% of all assists that year, mainly because he played in such a (relatively) small percentage of league games.

I guess my main point is that if you're trying to find the underlying scoring an era, you bias yourself much more by excluding a guy who was on the ice for probably 12-14% of all minutes played as opposed to excluding a guy who was on the ice for ~2% of all minutes played.

I'm also not a huge fan of adjusting assists and goals differently. I haven't seen any evidence to show that assists were inherently harder to get on a given goal in any era or that the variation in assists per goal is anything but random. If it exists I'd love to see it.

I'm also not a fan of the roster size adjustment. I really don't care if rosters have 10 skaters or 100. What really matters is how much time a guy played. Just because Howe played on a smaller roster doesn't mean he inherently got more ice time than Crosby, lines aren't rotated equally.

 

[Czech Your Math]

Personally, I have a few issues with this approach. I don't agree with excluding the player from era averages, especially when you're dealing with massively different league sizes. In the 52-53 season they chose, Gordie Howe made up just over 3% of *all* NHL assists, but he also played in 1/3 of all NHL games that season. In a 30 team league a player plays in 1/15th of league games. In 05-06 Thornton had 96 assists in 81 games, but that made up well under .8% of all assists that year, mainly because he played in such a (relatively) small percentage of league games.

I guess my main point is that if you're trying to find the underlying scoring an era, you bias yourself much more by excluding a guy who was on the ice for probably 12-14% of all minutes played as opposed to excluding a guy who was on the ice for ~2% of all minutes played.

Totally agree, and that's my main beef with their adjusted formulas.

I'm also not a huge fan of adjusting assists and goals differently. I haven't seen any evidence to show that assists were inherently harder to get on a given goal in any era or that the variation in assists per goal is anything but random. If it exists I'd love to see it.

The variation from season to season may be random, but the longer term trend has been for more assists per goal to be awarded. So I have to disagree with you on this.

I'm also not a fan of the roster size adjustment. I really don't care if rosters have 10 skaters or 100. What really matters is how much time a guy played. Just because Howe played on a smaller roster doesn't mean he inherently got more ice time than Crosby, lines aren't rotated equally.

I tend to agree with you on this.

 

[hatterson]

The variation from season to season may be random, but the longer term trend has been for more assists per goal to be awarded. So I have to disagree with you on this.

Fair enough, I haven't looked at it on anything more that a recent basis (post 04 lockout) and didn't notice anything then. Do you know a good place I can view league wide assist numbers (or assists per goal) going back through time?

 

[ted2019]

http://www.hockey-reference.com/about/adjusted_stats.html describes it in detail.

They have 3 adjustments:

- Schedule. Normalize everything to 82 game seasons by dividing totals by season length and multiplying by 82.
- League scoring. For goals, normalize everything to 6 goals per game by dividing league wide goals per game *without* the player in question and multiplying by 6. For assists, normalize everything to 10 assists per game (6 goals * 1.67 assists per goal) by dividing by league wide assists per game *without* the player in question and multiplying by 10. For points, simply add adjusted goals and adjusted assists.
- Roster size. Adjust to an 18 skater roster by dividing allowed roster size in a season by 18. Theoretically this is to account for a player making up a larger percentage of his team and thus being expected to make up a larger percentage of the scoring.


Personally, I have a few issues with this approach. I don't agree with excluding the player from era averages, especially when you're dealing with massively different league sizes. In the 52-53 season they chose, Gordie Howe made up just over 3% of *all* NHL assists, but he also played in 1/3 of all NHL games that season. In a 30 team league a player plays in 1/15th of league games. In 05-06 Thornton had 96 assists in 81 games, but that made up well under .8% of all assists that year, mainly because he played in such a (relatively) small percentage of league games.

I guess my main point is that if you're trying to find the underlying scoring an era, you bias yourself much more by excluding a guy who was on the ice for probably 12-14% of all minutes played as opposed to excluding a guy who was on the ice for ~2% of all minutes played.

I'm also not a huge fan of adjusting assists and goals differently. I haven't seen any evidence to show that assists were inherently harder to get on a given goal in any era or that the variation in assists per goal is anything but random. If it exists I'd love to see it.

I'm also not a fan of the roster size adjustment. I really don't care if rosters have 10 skaters or 100. What really matters is how much time a guy played. Just because Howe played on a smaller roster doesn't mean he inherently got more ice time than Crosby, lines aren't rotated equally.

I wanted to use the formula for the HOH Top 60 Centers project. Also, I wanted to come up with a list of the top 30 or so at each position. It seems like more work then it's worth.

 

[matnor]

Fair enough, I haven't looked at it on anything more that a recent basis (post 04 lockout) and didn't notice anything then. Do you know a good place I can view league wide assist numbers (or assists per goal) going back through time?

I attach two graphs showing average amount of assists per goal, one over the entire history of the NHL and one post expansion. As you can see, the assist per goal ratio has been steadily increasing.

 

[Hagged]

In a league where for example turnovers are more common, the assists credited per goal scored would be lower, even if the criteria for assists remained the same.

In that sense, in a league with more talent and a more structured game you could expect a higher number of assists.