Year	Percent
1960	4.2306
1961	4.23512
1962	4.23554
1963	4.25052
1964	4.26273
1965	4.26904
1966	4.28381
1967	4.28948
1968	4.27345
1969	4.25916
1970	4.22487
1971	4.20485
1972	5.13763
1973	5.3741
1974	5.32869
1975	5.27465
1976	5.22001
1977	5.14916
1978	5.1046
1979	5.05412
1980	5.0168
1981	5.50365
1982	5.71777
1983	5.63378
1984	5.53644
1985	5.40954
1986	5.29156
1987	5.17627
1988	5.07305
1989	4.96469
1990	4.87957
1991	5.04618
1992	5.08175
1993	4.96761
1994	4.8668
1995	4.76096
1996	4.6523
1997	4.54239
1998	4.45822
1999	4.3818
2000	4.31687
2001	3.23475
2002	3.2078
2003	3.17919
2004	3.15417
2005	3.11711
2006	3.08697
2007	3.0525
2008	3.02043
2009	2.9776
2010	2.89643
2011	2.65919
2012	2.6212
2013	2.57284
2014	2.52238
2015	2.4609
2016	2.39751
2017	2.32873