Year	Percent
1960	4.35063
1961	4.18523
1962	4.16918
1963	4.12065
1964	4.05124
1965	3.96363
1966	3.87318
1967	3.79625
1968	3.74394
1969	3.71548
1970	3.81719
1971	4.42697
1972	4.41138
1973	4.38111
1974	4.35082
1975	4.2312
1976	3.78355
1977	3.75384
1978	3.73507
1979	3.72629
1980	3.97718
1981	5.21752
1982	5.18097
1983	5.13497
1984	5.08904
1985	5.02588
1986	4.97562
1987	4.91795
1988	4.84867
1989	4.75967
1990	4.29065
1991	2.30776
1992	2.25395
1993	2.20935
1994	2.16963
1995	2.1346
1996	2.09706
1997	2.05722
1998	2.02155
1999	1.99092
2000	1.96178
2001	1.93895
2002	1.91043
2003	1.85884
2004	1.77818
2005	1.68116
2006	1.57764
2007	1.48951
2008	1.43322
2009	1.42078
2010	1.53358
2011	2.05986
2012	2.0702
2013	2.06984
2014	2.04588
2015	2.01312
2016	1.97632
2017	1.9791