Year	Percent
1960	14.72166
1961	13.79193
1962	12.19517
1963	12.34357
1964	12.61192
1965	10.40255
1966	15.07574
1967	11.46015
1968	14.29087
1969	14.37295
1970	15.81706
1971	16.67885
1972	14.76684
1973	14.39381
1974	15.50945
1975	14.07032
1976	13.90272
1977	13.26762
1978	13.74401
1979	13.45876
1980	15.5782
1981	15.43293
1982	15.1764
1983	13.22796
1984	12.47218
1985	12.52547
1986	11.99339
1987	12.91871
1988	13.8603
1989	13.81661
1990	14.82095
1991	13.90831
1992	15.7571
1993	18.75933
1994	20.91918
1995	20.96349
1996	20.84465
1997	20.75552
1998	20.90157
1999	17.8027
2000	16.75195
2001	18.51398
2002	18.16707
2003	19.94088
2004	19.09268
2005	18.78432
2006	20.53644
2007	19.79066
2008	20.26258
2009	18.24919
2010	17.76486
2011	19.93276
2012	20.03734
2013	20.12605
2014	21.38324
2015	23.37285
2016	21.7081
2017	20.0869