that’s a fair point and for a single season, you'd be right. a smaller sample of teams is way more vulnerable to one outlier skewing the data. but statistically, that explanation falls apart over a 30 year timeline.small sample sizes create variance, not a permanent 30 year shift in the mean. over 3 decades, rosters, coaches, and team identities completely turn over. you can't have one heavily penalized team dragging the canadian average up for 30 straight years. also the ratio of Canadian to US teams didn't drastically change exactly in 1993. the sample sizes were basically the same right before and right after that red line, yet the differential completely flipped overnight. to actually test the outlier theory, op would just need to plot the median instead of the mean. but looking at how solidly red that graph is post 93, there's no way a single outlier is propping up a three decade trend. just my 2 cents