Analysis of American Caving Accidents 2021

I've been looking forward to the release of the American Caving Accidents 2021. Many rescues and noteworthy events occurred in the Upper Cumberland of Tennessee (5 out of 17!) and even more involved rescuers that I'm friends with. Looking at the data provided by the ACA editor, I produced a few graphs and did some basic analysis. Because I know I'll be asked, I'll explain in greater detail what the final charts represent. Basically one could think of it as a means of outlier detection. It's similar to a chi squared analysis, but instead of looking for significance, one looks for interesting patterns. For example in the chart Difference of Observed and Expected Caving Accidents by Type, between 1986 and 1994 numerous equipment problems are being documented. But around 1994, the problem seems to be resolved. What happened? Did equipment technology change in those years? This analysis shows the "peaks and troughs" compared to the harmonic mean of the data.