Year	Percent
1960	3.67107
1961	6.7867
1962	7.97011
1963	6.97425
1964	5.4672
1965	5.39535
1966	5.66483
1967	4.96454
1968	5.07937
1969	4.73744
1970	6.36132
1971	8.24742
1972	8.54376
1973	9.09341
1974	11.27471
1975	11.23177
1976	10.66569
1977	10.70719
1978	7.2887
1979	5.88172
1980	11.92789
1981	12.9047
1982	15.01687
1983	16.55784
1984	19.6735
1985	18.96625
1986	16.10202
1987	17.75744
1988	17.55286
1989	17.78075
1990	17.57789
1991	16.63488
1992	17.34513
1993	19.34328
1994	20.38372
1995	24.35103
1996	27.82666
1997	30.38861
1998	19.70601
1999	18.82376
2000	22.55183
2001	22.82091
2002	22.99984
2003	23.35834
2004	25.3692
2005	24.41936
2006	26.50069
2007	26.06936
2008	27.08007
2009	23.3588
2010	25.45041
2011	30.40053
2012	28.57794
2013	28.07807
2014	27.64977
2015	25.95394
2016	24.85056
2017	29.3327