Year	Percent
1972	2.19807
1973	3.76415
1974	4.53146
1975	4.28606
1976	3.48156
1977	3.74592
1978	3.62108
1979	3.80043
1980	4.69611
1981	6.25546
1982	6.44931
1983	5.38198
1984	4.57565
1985	4.30422
1986	4.12128
1987	3.03942
1988	3.15665
1989	3.52913
1990	3.5274
1991	2.39471
1992	2.84951
1993	2.7924
1994	2.57771
1995	2.71464
1996	2.80594
1997	2.39972
1998	2.25813
1999	2.39446
2000	2.43598
2001	2.50258
2002	2.53014
2003	2.23755
2004	2.04073
2005	2.00039
2006	2.00618
2007	1.77717
2008	1.86952
2009	1.82261
2010	1.87581
2011	1.71975
2012	1.80367
2013	1.81655
2014	1.80743
2015	1.82059
2016	1.88304
2017	2.05163