Year	Percent
1971	30.23837
1972	29.97677
1973	25.60265
1974	23.41245
1975	27.05317
1976	22.00678
1977	15.09752
1978	16.61173
1979	16.40078
1980	17.13621
1981	14.33908
1982	9.03652
1983	10.10731
1984	13.75335
1985	12.32478
1986	10.26203
1987	13.63035
1988	15.35409
1989	16.99786
1990	16.95436
1991	15.59759
1992	15.45346
1993	16.04904
1994	16.32904
1995	16.86929
1996	17.45522
1997	18.56584
1998	16.91756
1999	20.7002
2000	19.71456
2001	17.56905
2002	16.19384
2003	15.52782
2004	15.31737
2005	14.59643
2006	13.99146
2007	13.39057
2008	12.14616
2009	10.43093
2010	9.16035
2011	10.06969
2012	10.33449
2013	9.52953
2014	8.94122
2015	8.51745
2016	8.19597