Year	Percent
1960	5.50272
1961	5.48952
1962	5.48568
1963	5.48251
1964	5.49381
1965	5.49338
1966	5.49032
1967	5.48494
1968	5.48703
1969	5.49194
1970	5.51382
1971	5.40105
1972	5.41822
1973	5.35197
1974	5.21079
1975	5.01864
1976	4.56444
1977	3.43709
1978	3.39403
1979	3.46172
1980	3.60737
1981	3.76263
1982	3.88404
1983	3.97358
1984	4.01842
1985	4.0177
1986	4.01301
1987	4.01007
1988	3.94778
1989	3.42377
1990	3.41384
1991	3.41492
1992	3.39847
1993	3.3339
1994	3.22305
1995	3.07603
1996	2.92784
1997	2.8052
1998	2.74167
1999	2.74401
2000	2.79367
2001	2.85876
2002	2.90864
2003	3.31656
2004	3.628
2005	3.64276
2006	3.6571
2007	3.67525
2008	3.7086
2009	3.7581
2010	3.81938
2011	3.87839
2012	3.91677
2013	3.92462
2014	3.89289
2015	3.85238
2016	3.80248
2017	3.76286