Year	Percent
1978	4.0134
1979	3.3143
1980	3.3654
1981	3.8037
1982	6.0719
1983	7.1518
1984	7.0332
1985	8.0688
1986	7.9893
1987	6.2162
1988	5.6851
1989	5.3731
1990	5.8917
1991	5.3485
1992	5.4927
1993	4.8173
1994	4.6774
1995	5.3922
1996	7.1429
1997	7.2041
1998	8.1416
1999	8.0895
2000	8.3051
2001	11.5453
2002	13.9665
2003	13.5081
2004	13.0879
2005	11.6631
2006	11.5124
2007	11.5473
2008	12.5
2009	15.641
2010	13.5678
2011	12.6238
2012	12.5908
2013	13.2251
2014	13.1222
2015	12.4183
2016	11.7284
2017	11.5464