Year	Percent
1960	13.84908
1961	13.73215
1962	14.49736
1963	15.33101
1964	16.39828
1965	16.15027
1966	16.29439
1967	17.29654
1968	17.47919
1969	18.02808
1970	18.46554
1971	23.10522
1972	22.94746
1973	33.44008
1974	47.37093
1975	40.73574
1976	37.205
1977	30.7953
1978	23.47454
1979	26.74634
1980	13.73603
1981	12.36972
1982	17.09027
1983	14.53382
1984	11.31344
1985	8.8836
1986	3.73162
1987	9.1574
1988	7.28516
1989	9.82727
1990	13.27874
1991	13.82432
1992	13.16459
1993	25.41011
1994	28.28619
1995	21.67624
1996	20.19513
1997	17.27793
1998	12.68338
1999	19.29202
2000	21.46706
2001	19.30332
2002	24.4139
2003	24.62747
2004	25.26693
2005	30.33082
2006	29.86904
2007	28.84361
2008	26.57713
2009	22.71149
2010	24.39965
2011	25.63295
2012	24.12886
2013	26.88186
2014	23.14086
2015	19.74339
2016	22.40403
2017	23.78679