Year	Percent
1960	8.5118
1961	8.6545
1962	9.06245
1963	9.35048
1964	8.54238
1965	8.36351
1966	10.49895
1967	9.93638
1968	8.9447
1969	9.06415
1970	7.88293
1971	8.15686
1972	9.12991
1973	11.6375
1974	14.21571
1975	14.14166
1976	14.04868
1977	13.98023
1978	13.65273
1979	15.17378
1980	19.32408
1981	21.38946
1982	17.2091
1983	16.47614
1984	16.80096
1985	16.1338
1986	17.69452
1987	18.12408
1988	16.31458
1989	15.94575
1990	14.77859
1991	14.19964
1992	14.87884
1993	14.04777
1994	14.44561
1995	14.42528
1996	14.28696
1997	16.22227
1998	16.29658
1999	19.25608
2000	23.71838
2001	22.78874
2002	20.11285
2003	18.54458
2004	20.70811
2005	21.31223
2006	21.17401
2007	22.52027
2008	23.36157
2009	18.98219
2010	22.10221
2011	25.53542
2012	28.68399
2013	30.35343
2014	32.37304
2015	31.72264
2016	30.45873
2017	33.21994