Year

Number of Attacks¹

Percent

Mean

Variance

Standard Deviation

Coefficient of Variation

2007

1

4.00%

2.5

2.25

1.50

0.60

2008

7

28.00%

20.25

4.50

1.80

2009

3

12.00%

0.25

0.50

0.20

2010

0

0.00%

6.25

2.50

1.00

2011

2

8.00%

0.25

0.50

0.20

2012

2

8.00%

0.25

0.50

0.20

2013

1

4.00%

2.25

1.50

0.60

2014

4

16.00%

2.25

1.50

0.60

2015

2

8.00%

0.25

0.50

0.20

2016

3

12.00%

0.25

0.50

0.20

Sum

25

Average

3.45

1.86

0.74