Year	Percent
1960-01-01	23.230
1961-01-01	22.990
1962-01-01	21.580
1963-01-01	22.380
1964-01-01	21.530
1965-01-01	21.370
1966-01-01	22.910
1967-01-01	22.740
1968-01-01	22.880
1969-01-01	22.815
1970-01-01	23.340
1971-01-01	24.245
1972-01-01	25.940
1973-01-01	26.970
1974-01-01	25.120
1975-01-01	26.850
1976-01-01	26.945
1977-01-01	29.580
1978-01-01	30.640
1979-01-01	31.370
1980-01-01	32.595
1981-01-01	34.980
1982-01-01	34.890
1983-01-01	36.670
1984-01-01	37.460
1985-01-01	37.820
1986-01-01	38.950
1987-01-01	38.960
1988-01-01	38.150
1989-01-01	37.280
1990-01-01	37.340
1991-01-01	36.985
1992-01-01	37.150
1993-01-01	37.055
1994-01-01	34.490
1995-01-01	35.975
1996-01-01	34.800
1997-01-01	35.700
1998-01-01	38.380
1999-01-01	38.355
2000-01-01	37.845
2001-01-01	39.030
2002-01-01	40.520
2003-01-01	41.310
2004-01-01	41.055
2005-01-01	40.650
2006-01-01	41.570
2007-01-01	43.415
2008-01-01	45.095
2009-01-01	49.380
2010-01-01	47.910
2011-01-01	47.060
2012-01-01	47.520
2013-01-01	49.500
2014-01-01	52.660
2015-01-01	56.115