Year	Percent
1960	7.36894
1961	7.52
1962	7.552
1963	7.56248
1964	7.54308
1965	7.54977
1966	7.50729
1967	7.52234
1968	7.58483
1969	7.71487
1970	6.24278
1971	4.08528
1972	4.22797
1973	4.30343
1974	4.28551
1975	4.20573
1976	5.23663
1977	6.88603
1978	6.79452
1979	6.73536
1980	6.67578
1981	6.6231
1982	6.55358
1983	6.46755
1984	6.36264
1985	6.23767
1986	6.12027
1987	4.95163
1988	4.19922
1989	4.17679
1990	4.19706
1991	4.21922
1992	4.22524
1993	4.22965
1994	4.2304
1995	4.21066
1996	4.19899
1997	4.18001
1998	4.15305
1999	4.12091
2000	4.74561
2001	5.11186
2002	5.07106
2003	5.01472
2004	4.94827
2005	4.86899
2006	4.79203
2007	4.71838
2008	4.66123
2009	4.60307
2010	4.55938
2011	4.48441
2012	4.41217
2013	4.33339
2014	4.2423
2015	4.15721
2016	4.06073
2017	3.97814