Year	Percent
1960	2.84573
1961	2.84919
1962	2.85707
1963	2.90141
1964	2.99415
1965	3.10117
1966	3.24053
1967	3.32134
1968	3.23263
1969	2.94096
1970	2.53837
1971	2.09477
1972	1.75009
1973	1.60503
1974	1.72219
1975	2.01367
1976	2.34682
1977	2.6052
1978	2.77453
1979	2.81957
1980	2.78049
1981	2.72476
1982	2.69395
1983	2.67406
1984	2.6741
1985	2.68322
1986	2.69153
1987	2.6808
1988	2.64065
1989	2.56538
1990	2.46872
1991	2.3627
1992	2.26835
1993	2.1993
1994	2.16396
1995	2.1497
1996	2.13594
1997	2.10921
1998	2.07223
1999	2.02117
2000	1.95819
2001	1.90147
2002	1.84226
2003	1.75488
2004	1.63277
2005	1.49165
2006	1.34137
2007	1.21105
2008	1.12632
2009	1.10199
2010	1.11989
2011	1.15195
2012	1.17243
2013	1.17732
2014	1.15719
2015	1.12014
2016	1.08017
2017	1.0489