Changes in the F/EF Scale in the Modern Era

I just posted the following graphic on Facebook:

I was interested in seeing how tornado damage has changed in the modern era defined as 1990-2012, the years that Doppler radar has been used for warning on severe thunderstorms that can or have produced tornadoes.  It's interesting to see that the tornado damage of EF5 was used 18 times since 1990.  Now, I need to put a little asterisk here seeing that the National Weather Service has only used the Enhanced Fujita Scale since February 2007, with the damage from the Greensburg, KS tornado being the first EF5.  So, actually, out of those 18 F5/EF5 damage tornadoes, only 8 tornadoes carry the illustrious EF5 moniker, while the others were rated F5 damage.

Now, F5 and EF5 are supposed to be similar ratings in order to protect the climatological record.  The F-Scale is a 1/4-mile wind originally used by Fujita (1971), while the EF-Scale is a 3-sec wind.  If you want all the juicy details see the Storm Prediction site at spc.noaa.gov/efscale.  

The EF-Scale is to take into consideration structural integrity and lately there has been discussion whether the Joplin tornado was worthy of the EF5 designation, see Mike Smith's blog here.  The fact remains that the EF-Scale, like its father, the F-Scale is subjective and carries an error of +/-1.  In most areas, this may seem trivial, but scientifically can mean the difference in an accurate database.

Now, for comparison, let's look at how the F-Scale faired from 1972-1989, prior to Doppler radar being widely used:

Note that from the inception of the F-Scale, which was widely used to survey the Super Outbreak of April 3-4, 1974, really for the first time, 0.10% of all tornado damage was rated F5.  Compare that to the modern era of 0.06% being rated F5/EF5 and it is pretty comparable, and this dataset includes Super Outbreak II that occurred April 24-28, 2011.