Year	Percent
1960-01-01	4.130
1961-01-01	4.445
1962-01-01	5.000
1963-01-01	5.030
1964-01-01	4.370
1965-01-01	4.310
1966-01-01	3.950
1967-01-01	4.075
1968-01-01	5.030
1969-01-01	4.280
1970-01-01	4.240
1971-01-01	5.230
1972-01-01	5.040
1973-01-01	6.030
1974-01-01	5.665
1975-01-01	5.960
1976-01-01	6.025
1977-01-01	7.095
1978-01-01	7.335
1979-01-01	7.380
1980-01-01	8.520
1981-01-01	9.210
1982-01-01	9.010
1983-01-01	10.230
1984-01-01	11.280
1985-01-01	8.340
1986-01-01	7.875
1987-01-01	7.530
1988-01-01	8.280
1989-01-01	9.150
1990-01-01	8.620
1991-01-01	7.865
1992-01-01	9.200
1993-01-01	7.680
1994-01-01	6.640
1995-01-01	6.895
1996-01-01	6.880
1997-01-01	5.720
1998-01-01	6.090
1999-01-01	6.215
2000-01-01	5.860
2001-01-01	5.550
2002-01-01	6.060
2003-01-01	5.100
2004-01-01	3.890
2005-01-01	3.435
2006-01-01	3.490
2007-01-01	3.925
2008-01-01	3.700
2009-01-01	4.240
2010-01-01	4.370
2011-01-01	3.790
2012-01-01	4.770
2013-01-01	5.790
2014-01-01	6.580
2015-01-01	6.140