OK, I know I promised the next post was on engines, but I got sidetracked…

Being the data geek that I am, I was really curious if the decreasing number of cautions was specific to this year.  It’s not:  Cautions have been decreasing since 2005,as the graph below shows.  The squares are the cumulative number of cautions per 100 miles, obtained by adding up all the cautions in a season and dividing by the total number of miles in the races.  (This is a more accurate number than total cautions, given rainouts, shortening races and different venues from year to year.)

The straight line is a linear regression, with a R-squared of 0.87, which is pretty good.  The grey box in the lower right hand corner is what the fit predicts the number of cautions should be if the trend continues.

Of course, someone is wondering what happened before 2005. The trend was totally opposite.

My rationale for going back to 2001 is that this was the first 36-race season.  Not a great reason, but that was pretty much it.  The peak number of cautions was in 2005.  What happened in 2006 that sent the number of cautions down?