Year	Percent
1979	3.4284
1980	2.9398
1981	3.4815
1982	3.7795
1983	6.8153
1984	6.3617
1985	7.0491
1986	6.1089
1987	6.7859
1988	6.8428
1989	6.0982
1990	6.4695
1991	9.6216
1992	11.8067
1993	13.701
1994	11.5067
1995	9.2498
1996	9.028
1997	7.9717
1998	7.251
1999	6.534
2000	5.3196
2001	5.5434
2002	5.1277
2003	4.2511
2004	3.8857
2005	3.6994
2006	3.5475
2007	2.8142
2008	3.0552
2009	3.7035
2010	3.7271
2011	3.6713
2012	3.7246
2013	4.3416
2014	4.3179
2015	4.8293
2016	4.8123
2017	4.3728