Year	Percent
1971	12.86745
1972	15.52636
1973	15.7476
1974	13.64199
1975	10.31904
1976	5.81548
1977	6.17651
1978	6.32046
1979	7.18495
1980	7.25205
1981	6.33987
1982	2.06041
1983	5.14549
1984	8.43927
1985	5.8507
1986	6.60203
1987	12.48669
1988	6.36489
1989	7.16923
1990	9.76712
1991	15.80468
1992	17.04805
1993	19.18713
1994	4.60379
1995	10.2232
1996	12.39152
1997	19.38426
1998	19.89213
1999	18.94834
2000	23.3205
2001	26.98028
2002	32.21864
2003	37.20038
2004	38.69769
2005	43.38385
2006	44.73952
2007	44.47566
2008	48.21112
2009	51.66406
2010	49.03653
2011	51.13642
2012	47.83579
2013	44.33833
2014	44.24467
2015	41.64683
2016	42.10831