Year	Percent
1960	23.47923
1961	27.76645
1962	21.73094
1963	18.27288
1964	21.47391
1965	22.42768
1966	20.54255
1967	21.21504
1968	21.6905
1969	23.99061
1970	24.4401
1971	24.11303
1972	23.89154
1973	20.89381
1974	22.26033
1975	29.44105
1976	30.72944
1977	30.94169
1978	27.80016
1979	25.85677
1980	25.25779
1981	22.69109
1982	21.75495
1983	20.88775
1984	19.96409
1985	17.58907
1986	17.46176
1987	19.55487
1988	18.64004
1989	15.5147
1990	13.99698
1991	14.63698
1992	16.70241
1993	19.05643
1994	19.93892
1995	17.93781
1996	18.08214
1997	19.37016
1998	19.93497
1999	18.01397
2000	16.1927
2001	14.17918
2002	11.96062
2003	15.13755
2004	17.55127
2005	18.88826
2006	18.68049
2007	20.09911
2008	19.57278
2009	16.05311
2010	17.70553
2011	18.39846
2012	16.50199
2013	17.30578
2014	17.26288
2015	17.0707
2016	17.02702
2017	19.0734