Trend That Is Not A Trend: Changes in Data Definition or Measurement Technology
This chart illustrates a data analysis mistake that is absolutely endemic to many of the most famous climate charts. Marc Morano screencapped this from a new EPA web site (update: Actually originally from Pat Michaels at Cato)
The figure below is a portion of a screen capture from the “Heat-Related Deaths” section of the EPA’s new “Climate Change Indicators” website. It is labeled “Deaths Classified as ‘Heat-Related’ in the United States, 1979–2010.”
The key is in the footnote, which says
Between 1998 and 1999, the World Health Organization revised the international codes used to classify causes of death. As a result, data from earlier than 1999 cannot easily be compared with data from 1999 and later.
So, in other words, this chart is totally bogus. There is an essentially flat trend up to the 1998 switch in data definition and an essentially flat trend after 1998. There is a step-change upwards in 1998 due to the data redefinition. This makes this chart useless unless your purpose is to fool generally ignorant people that there is an upwards trend, and then it is very useful. It is not, however, good science.
Other examples of this step change in a metric occurring at a data redefinition or change in measurement technique can be found in
- The hockey stick (and here)
- Ocean heat content (sorry, can't find the link but the shift from using thermometers in pails dipped from ships to the ARGO floats caused a one time step change in ocean heat content measurements)
- Tornadoes
- Hurricanes
