League Translations

How difficult is it to score a goal in the National Hockey League (NHL) relative to another league? With half of NHL players coming from the minor leagues, a quarter from European Elite Leagues, 20% coming directly from Canadian Major Junior and 10% from the NCAA, that’s a question NHL teams try to answer every day. In evaluating these players, it is critical to know how a player’s performance translates to the NHL.

One way to evaluate the difficulty of one league relative to another is examine the relative performance of players who have played in both leagues. Players rarely play significant time in two leagues in the same year, but they often play in one league in one year and in another the next. As long as a player’s skill level is approximately constant over this two year period, the ratio of his performance in each league can be used to estimate the relative difficulty of the two leagues.

Historically, the only statistics available are goals, assists and games played. With so little data, the best quantity to compare is a player’s Point-Per-Game rate (PPG). The difficulty of a league relative to the NHL can be determined by dividing the PPG that a player had in that league in one year by the PPG he had in the NHL the next year, or vice-versa. The PPG should be adjusted for the assist per goal rate in each league since European leagues don’t award a second assist as often as the NHL does.

Minor Leagues

NHL teams have traditionally had minor-league affiliates in the American Hockey League (AHL) and the International Hockey League (IHL). The IHL was absorbed into the AHL in 2002, and all AHL teams are now affiliated with NHL teams.

	Difficulty	N
AHL	0.44	384
IHL	0.43	113

This method tends to underestimate the difficulty of leagues that are substantially weaker than the NHL. This happens because only the top players get called up to the NHL – before the call-up, they were on the first line and playing the power play; after the call-up, they’re 3^rd or 4^th liners. This cuts down on both their overall ice time, and on their power play time, which is when they’d get the best opportunities to score.

We can improve this estimate by considering only even-strength goals:

71 players	PPG	ESG/G
AHL 2002-03	0.83	0.20
NHL 2003-04	0.34	0.11
Ratio	0.41	0.54

European Elite Leagues

European players did not enter the NHL on a large-scale until the early 1990s:

League	Difficulty	N
Russian Elite League	0.83	101
Swedish Elite League	0.78	77
Czech Republic League	0.74	53
Finland SM-Liiga	0.54	76
Deutsche Eishockey League	0.52	74
Switzerland National League	0.43	30

These results are not unexpected given the performance of each country’s national team in the Canada Cup and World Cup of Hockey over the last thirty years:

Team	WPCT
Russia/CIS/USSR	0.649
Sweden	0.540
Czech Republic	0.478
Finland	0.305
Germany	0.144

Canada	0.681
United States	0.562

Given that the best team outside of North America (Russia/USSR) has a lower winning percentage than the Canadian National Team, it is not surprising that the Russian Elite League, where most players are Russian, has a lower league difficulty than the NHL, where most of the players have historically been Canadian, and which now selects players from throughout the world.

Major Junior and College Leagues

Most young players don’t jump directly from Major Junior hockey to the NHL, and instead spend a year or more in the minors. The league difficulties for the top three Junior leagues are shown below:

	WHL	N	OHL	N	QMJHL	N
Junior to AHL	0.43	302	0.45	295	0.41	135
Junior to NHL	0.30	143	0.30	205	0.28	62
Implied AHL to NHL	0.70		0.67		0.68
Observed AHL to NHL	0.65	154

Only 18- and 19-year-old players were included in the AHL to NHL analysis. Note that the AHL league difficulty (~0.68) is higher for 18- and 19-year-olds than it is for players of all ages. This is because young players tend to improve substantially from one year to the next, while older players have reached their peak level of ability. Young players, as a group, will do much better in their next year in the NHL, which makes the AHL appear better than it actually is.

The difficulty of all three junior leagues is about the same. Also, the difficulty of each junior league with respect to the NHL (~0.30) is the same as the difficulty experienced by players who went from junior to the NHL via the minors, which validates the concept.

The next largest source of NHL players is the NCAA:

	Difficulty	N
NCAA	0.41	295

Since NCAA players lose college eligibility if they declare for the NHL Draft, they do not typically opt-in to the draft until age 21 or 22. The NCAA league difficulty is not then affected by the skills improvement seen in teenage players.

The World Hockey Association

The World Hockey Association (WHA) was a North American professional league that operated from 1972 to 1979. Initially it competed against the NHL for the best players, but it ultimately went bankrupt and its remaining teams were absorbed into the NHL. The WHA league difficulty is shown below:

Year	72-73	73-74	74-75	75-76	76-77	77-78	78-79
WHA	0.46	0.76	0.70	0.88	0.55	0.65	0.89
N	39	20	21	16	10	14	59

In its first season, 1972-73, the WHA league difficulty was 0.46, which is barely better than the minors. This is not surprising since 39 former NHL players played in the 12-team WHA in its inaugural season, while 200 minor league players filled out the rosters.

During 1973-75, the WHA stole away top NHL draft picks, recruited more established NHL players, and signed skilled European players. The WHA league difficulty ranged from 0.7 to 0.88 during those three years. However, beginning in 1976, the balance swung back in the NHL’s direction, and the league difficulty suffered as a result. In its final year of operation, the WHA was almost as good as the NHL – 59 players moved to the NHL after the last season, and their performance implied a WHA league difficulty of 0.89.

Summary

The league difficulty for the largest NHL feeder leagues is shown below:

League	Difficulty	N
NHL	1.00
WHA Final Year (1978-79)	0.89	59
Russian Elite League	0.83	101
Swedish Elite League	0.78	77
Czech Republic League	0.74	53
Finland SM-Liiga	0.54	76
Deutsche Eishockey League	0.52	74
WHA First Year (1972-73)	0.46	39
AHL	0.44	384
IHL	0.43	113
Switzerland National League	0.44	30
NCAA	0.41	295
Canadian Major Junior	0.29*	410

* The difficulty of Canadian Major Junior is lower than predicted by this method since major junior players are 20 years old or younger and consequently experience significant skills growth from year-to-year.