Year	Percent
1960-01-01	12.230
1961-01-01	12.160
1962-01-01	12.570
1963-01-01	13.570
1964-01-01	14.030
1965-01-01	14.610
1966-01-01	15.095
1967-01-01	14.935
1968-01-01	16.125
1969-01-01	16.655
1970-01-01	17.460
1971-01-01	17.740
1972-01-01	18.910
1973-01-01	17.900
1974-01-01	17.350
1975-01-01	19.540
1976-01-01	20.350
1977-01-01	22.390
1978-01-01	23.880
1979-01-01	23.750
1980-01-01	24.300
1981-01-01	25.595
1982-01-01	27.000
1983-01-01	28.110
1984-01-01	25.535
1985-01-01	24.930
1986-01-01	26.430
1987-01-01	26.190
1988-01-01	27.190
1989-01-01	27.685
1990-01-01	24.515
1991-01-01	23.620
1992-01-01	21.830
1993-01-01	21.435
1994-01-01	21.265
1995-01-01	21.640
1996-01-01	22.225
1997-01-01	23.105
1998-01-01	23.390
1999-01-01	25.120
2000-01-01	26.325
2001-01-01	26.120
2002-01-01	25.230
2003-01-01	25.070
2004-01-01	25.055
2005-01-01	26.480
2006-01-01	26.740
2007-01-01	30.725
2008-01-01	34.210
2009-01-01	38.470
2010-01-01	38.190
2011-01-01	37.320
2012-01-01	37.950
2013-01-01	38.910
2014-01-01	41.820
2015-01-01	44.540