Year	Percent
1960	6.80698
1961	6.56652
1962	6.53051
1963	6.58115
1964	6.85093
1965	6.82579
1966	7.14421
1967	7.01622
1968	7.43818
1969	7.50371
1970	7.95904
1971	7.92091
1972	8.47168
1973	10.12237
1974	13.57881
1975	12.71437
1976	13.27725
1977	13.59538
1978	14.08368
1979	15.52313
1980	16.85761
1981	15.94749
1982	14.0905
1983	13.07034
1984	14.11491
1985	13.1427
1986	13.27739
1987	13.93293
1988	14.88719
1989	15.14282
1990	15.22812
1991	15.06457
1992	15.32406
1993	15.52922
1994	16.44387
1995	17.68769
1996	17.86496
1997	18.4492
1998	17.89483
1999	18.16898
2000	19.84698
2001	17.96565
2002	17.24737
2003	17.61688
2004	19.06777
2005	20.11489
2006	21.2476
2007	21.88619
2008	23.48684
2009	18.4575
2010	21.70274
2011	24.15614
2012	24.03074
2013	23.417
2014	23.14189
2015	21.06911
2016	19.87258
2017	20.40277