Assists per Goal in the 1910s and Beyond

I was recently asked about assist rates in the first years that assists were officially awarded. As you may know, the PCHA began awarding assists in 1912/13, and the NHA followed a season later. And as you might also know, for many years very few assists were awarded per goal (as compared to modern standards). How few? This few:

It's possibly interesting to note that the NHA/NHL awarded fewer assists per goal than their western counterparts most every year (though their rate is less consistent). The possibly interesting part is whether this is simply due to slightly different standards in awarding assists, or whether it has to do with the fact that the PCHA still used the rover while the NHA did not. With more players available to participate in an offensive rush, perhaps it makes sense that more assists were awarded per goal.

It may be worth noting that when the PCHA finally dropped the rover after the 1921/22 season (as they began playing an interlocking schedule with the WCHL, which did not use the seventh man), its assist rate dropped from 0.57 to 0.51, and stayed at that level or lower, whereas in the final seven seasons with the rover, the PCHA had an assist rate of between 0.57 and 0.60 six times. This suggests to me that at least part of the reason that the NHA/NHL had a lower assist per goal rate is the lack of a fourth forward.

The first really big jump in assist rates occurred in in 1929/30. In 1928/29 there were 0.60 assists per goal, but there were 0.82 the following season. This is clearly due to the change in the forward passing rules that season, which made individual rushes less important and passing plays more important. The rate went to 0.92, then 1.05 in the next two seasons, and would never drop below that level again.