Year	Percent
1960	5.94085
1961	5.96058
1962	6.00569
1963	6.04232
1964	6.06874
1965	6.07538
1966	6.09825
1967	6.12
1968	6.13819
1969	6.13799
1970	6.15635
1971	8.70573
1972	8.65174
1973	8.57536
1974	8.52227
1975	8.45786
1976	7.75791
1977	5.56836
1978	5.58727
1979	5.60244
1980	5.62032
1981	5.62217
1982	5.62226
1983	5.61466
1984	5.60227
1985	5.57457
1986	5.54993
1987	5.29109
1988	4.57998
1989	4.51029
1990	4.43258
1991	4.35357
1992	4.28232
1993	4.19692
1994	4.11775
1995	4.03546
1996	3.95623
1997	3.88312
1998	3.84306
1999	3.83935
2000	3.85684
2001	3.87272
2002	3.89081
2003	3.90735
2004	3.92425
2005	3.93198
2006	3.94373
2007	3.95194
2008	3.95012
2009	3.9341
2010	3.91105
2011	3.88316
2012	3.85473
2013	3.82127
2014	3.78533
2015	3.74767
2016	3.70875
2017	3.66597