When do people worry about hurricanes?
I recently read an article in the December issue of Significance titled, “Does Christmas
really come earlier every year?” by Nathan Cunningham of the University
College of Dublin. His premise was that,
by using cluster analysis of Google Trends data, we can see how people have
begun thinking about the holidays earlier and earlier each year. It’s a good read: http://www.statslife.org.uk/significance/1892. I should note that Nathan graciously
answered my emails asking for clarification and saw real value in this
technique for emergency management work.
Google Trends
Google Trends (http://www.google.com/trends/)
allows you to view the volume of searches on particular terms. The units are percentage of total Google
searches. For example, the week that
Hurricane Katrina made landfall, “hurricane” scored almost 100; almost all
searches were hurricane related. If you sign-on with your Google ID, you can
also download the data to CSV. Cunningham
used Google Trends to analyze search volumes on holiday-related terms
(“Christmas”, “Santa Claus”, etc). Here
I’ve compared the search terms “hurricane” and “tornado”. You can see that there is a somewhat
repetitive pattern of increase mid-year.
I wanted to explore this pattern.Cluster Analysis
Cluster Analysis looks at data and organizes it into groups
that share similarities. Once Cunningham
had each year’s data, he used cluster analysis to determine in which week of
the year the volume of holiday-related searches began to increase. Similar analysis can be done on FEMA-related
search terms; a cluster analysis of the Google Trend data for the search term
“hurricane” reveals continuous periods of increased interest for the following
weeks from 2004-2014. This was simple to
implement using R (see code below). The
accompanying graphic shows the “shape” of the cluster; the x-axis is the week
number of the year, and the y-axis is the percentage of all Google searches for
the term “hurricane”. In hindsight, it
is possible to find explanations for these clusters; for example, 2005 and 2012
had periods of exceptionally high interest corresponding to the hurricane
activity of those years. 2009 and 2013
had little activity (look at the y-axis) corresponding to light years.

