Year	Percent
1960-01-01	13.610
1961-01-01	13.625
1962-01-01	13.560
1963-01-01	14.395
1964-01-01	14.960
1965-01-01	15.310
1966-01-01	15.700
1967-01-01	16.275
1968-01-01	16.415
1969-01-01	16.740
1970-01-01	17.870
1971-01-01	18.250
1972-01-01	19.055
1973-01-01	18.930
1974-01-01	18.060
1975-01-01	20.185
1976-01-01	20.960
1977-01-01	22.700
1978-01-01	24.185
1979-01-01	24.010
1980-01-01	24.330
1981-01-01	25.870
1982-01-01	27.410
1983-01-01	29.500
1984-01-01	26.495
1985-01-01	27.630
1986-01-01	27.300
1987-01-01	27.170
1988-01-01	27.865
1989-01-01	28.840
1990-01-01	27.815
1991-01-01	25.375
1992-01-01	24.290
1993-01-01	23.175
1994-01-01	22.905
1995-01-01	21.840
1996-01-01	23.145
1997-01-01	24.420
1998-01-01	24.390
1999-01-01	25.120
2000-01-01	26.675
2001-01-01	26.800
2002-01-01	26.070
2003-01-01	26.610
2004-01-01	25.550
2005-01-01	27.740
2006-01-01	28.295
2007-01-01	31.585
2008-01-01	34.600
2009-01-01	40.600
2010-01-01	40.540
2011-01-01	38.880
2012-01-01	39.910
2013-01-01	42.140
2014-01-01	43.890
2015-01-01	48.700