I was looking back at the toplists on MileSplit for the 1600m (including mile conversions) because I was curious how the top 50 of 2021 and 2022 compared to the top 50 of pre-Dragonfly years. The results were pretty much what I expected. From 2009-2019, the #50 time in the 1600 was anywhere from 4:09-4:11, with an average of 4:10.44 and a standard deviation of 0.69s (that's pretty consistent data). In 2021, that number dropped to 4:08.38, and in 2022 it was 4:07.41. For the folks at home, that means this year was ~FIVE standard deviations below the mean. Essentially, this means there is a 0% chance that this year's results came from a data set with the same mean. Something definitely changed, and the obvious answer is the shoes.
However, I came across another interesting tidbit of data while doing this. From 2000-2008 (MileSplit doesn't have data from before this), the mean #50 time was 4:14.36 with a standard deviation of 1.29s. This also suggests a 99% confidence that the 2009 results (a time of 4:11.64) comes from a data set with a different mean (i.e. there is some major factor dropping the times). Similarly to the pre/post-dragonfly time drop, the #50 time dropped almost 2 seconds from 2008 to 2009 alone. So what could have happened?
I had a hunch, and a quick internet search confirmed it. In the fall of 2008 (after the track season), the Nike Zoom Victory spike was released to the public. In other words: the 2009 track season was the very first season that saw high schoolers running in Nike Victory, AND there was a significant performance bump at the same time. Now, just like with the Dragonfly, there is no real way to prove causation. There are enough confounders that it's pretty much impossible to prove. But I found it very interesting, and I wonder why there was not a similar reaction to the shoes back then. They were first made available to select Nike athletes in 2007, and they were used by Webb to set his 3:46 American record (and by Lagat at the 2007 world championships, where he won double gold). This fact is never mentioned in discussion around Webb, but it has plagued every record setter of the past 2 years.