Year	Percent
1960	22.07904
1961	20.60946
1962	21.40673
1963	21.86354
1964	19.48239
1965	19.46309
1966	21.50538
1967	24.05322
1968	23.83749
1969	23.4763
1970	24.24618
1971	23.45191
1972	23.28725
1973	27.63736
1974	28.01733
1975	29.1297
1976	30.44118
1977	30
1978	23.19221
1979	23.1926
1980	24.8433
1981	25.66555
1982	22.49518
1983	20.75157
1984	28.37062
1985	24.19148
1986	22.91071
1987	25.45253
1988	23.3222
1989	18.77991
1990	23.78207
1991	23.27158
1992	23.20622
1993	16.1303
1994	29.63282
1995	30.36848
1996	22.82575
1997	21.35651
1998	32.77016
1999	28.02228
2000	25.60365
2001	27.99123
2002	15.86064
2003	20.17046
2004	18.84825
2005	18.12116
2006	17.63384
2007	23.31145
2008	22.65676
2009	20.02865
2010	22.78706
2011	20.77717
2012	26.2034
2013	35.65977
2014	33.70157
2015	29.15652
2016	32.96692
2017	29.16284