Year	Percent
1960	3.94097
1961	4.44779
1962	3.64674
1963	4.89813
1964	5.11048
1965	5.10389
1966	6.54034
1967	9.84338
1968	9.62348
1969	11.62941
1970	13.99247
1971	15.1478
1972	15.13439
1973	16.55211
1974	20.53034
1975	16.62836
1976	14.63397
1977	15.25428
1978	15.25986
1979	13.36612
1980	16.59073
1981	24.88996
1982	19.90058
1983	19.93909
1984	19.38427
1985	17.19161
1986	11.70499
1987	14.66453
1988	10.91996
1989	9.34457
1990	9.13901
1991	10.72525
1992	10.75301
1993	10.01778
1994	11.12841
1995	13.6205
1996	11.73439
1997	14.79073
1998	15.5157
1999	17.8933
2000	20.461
2001	18.38963
2002	17.17602
2003	22.27586
2004	21.62503
2005	24.48631
2006	24.70291
2007	29.25129
2008	31.27362
2009	22.0967
2010	22.11067
2011	25.62081
2012	29.21321
2013	27.39564
2014	24.40816
2015	25.08192
2016	24.93212
2017	28.47996