Year	Percent
1960	9.99669
1961	10.78235
1962	10.74675
1963	9.98349
1964	10.02841
1965	9.66272
1966	10.28428
1967	9.30614
1968	8.33081
1969	8.14599
1970	8.31311
1971	6.29149
1972	5.67473
1973	6.53941
1974	3.70108
1975	2.89508
1976	4.74608
1977	7.04075
1978	5.55766
1979	6.10922
1980	5.49428
1981	5.13086
1982	5.0753
1983	5.60385
1984	3.39626
1985	5.38448
1986	5.18293
1987	4.99005
1988	5.4283
1989	5.54014
1990	5.90832
1991	6.66261
1992	7.58668
1993	9.01727
1994	9.00154
1995	10.86463
1996	9.70651
1997	10.52037
1998	11.75733
1999	11.75864
2000	12.3442
2001	13.38656
2002	12.40997
2003	11.43115
2004	11.14651
2005	14.39284
2006	16.35346
2007	16.99533
2008	17.65886
2009	16.94013
2010	16.02411
2011	19.92207
2012	20.16159
2013	19.53787
2014	18.98966
2015	17.33667
2016	16.64972
2017	15.03611