Year	Percent
1960	12.81601
1961	12.82863
1962	12.11673
1963	13.39182
1964	12.07951
1965	12.66223
1966	11.67927
1967	11.5212
1968	12.37517
1969	12.807
1970	13.00433
1971	11.9431
1972	10.69484
1973	9.28759
1974	10.65752
1975	7.98173
1976	7.39999
1977	6.97716
1978	5.11443
1979	4.13506
1980	4.46967
1981	6.72998
1982	10.70034
1983	8.70406
1984	9.85599
1985	9.06206
1986	9.5976
1987	9.72063
1988	9.74789
1989	10.249
1990	10.41463
1991	11.55492
1992	12.45744
1993	12.26792
1994	12.82337
1995	13.10608
1996	14.70931
1997	15.93667
1998	16.43803
1999	17.84682
2000	21.43818
2001	21.16865
2002	22.9201
2003	22.67671
2004	20.86401
2005	23.51011
2006	22.76616
2007	25.07733
2008	25.76811
2009	20.19016
2010	18.12702
2011	20.1562
2012	21.30684
2013	20.63007
2014	20.41053
2015	20.00992
2016	20.67631
2017	19.98439