Database Reference
In-Depth Information
Figure 7-9. Simple control chart of annual earthquakes of magnitude 6.0 or greater
This version doesn't show any points “out of control,” or beyond three standard deviations
from the mean. If we change from
YEAR
to
MONTH
, then the control chart changes to show a
number of points above the 3 sigma line, including a sharp outlier in March 2011 corres-
ponding to the Great East Japan earthquake, as shown in
Figure 7-10
.