Created with Raphaël 2.1.2
0
2
4
6
8
10
12
14
16
18
20
0
1978
2
1979
1
1980
1
1981
20
1982
18
1983
17
1984
13
1985
3
1986
4
1987
2
1988
8
1989
1
1990
0
1991
2
1992
0
1993
7
1994
9
1995
11
1996
6
1997
5
1998
8
1999
0
2000
0
2001
1
2002
0
2003
3
2004
0
2005
2
2006
3
2007
7
2008
0
2009
0
2010
0
2011
0
2012
0
2013
0
2014
0
2015
0
2016
0
2017