Year	Percent
1961-01-01	15.320
1962-01-01	15.845
1963-01-01	16.270
1964-01-01	3.940
1965-01-01	3.480
1966-01-01	3.780
1967-01-01	4.090
1968-01-01	5.160
1969-01-01	5.520
1970-01-01	5.970
1971-01-01	5.780
1972-01-01	6.230
1973-01-01	7.210
1974-01-01	9.500
1975-01-01	11.710
1976-01-01	9.630
1977-01-01	9.060
1978-01-01	9.210
1979-01-01	8.490
1980-01-01	8.090
1981-01-01	7.690
1982-01-01	7.360
1983-01-01	7.740
1984-01-01	7.940
1985-01-01	7.150
1986-01-01	7.420
1987-01-01	7.570
1988-01-01	13.835
1989-01-01	20.100
1990-01-01	20.950
1991-01-01	22.800
1992-01-01	23.160
1993-01-01	24.825
1994-01-01	25.085
1995-01-01	24.655
1996-01-01	26.560
1997-01-01	27.740
1998-01-01	27.670
1999-01-01	48.360
2000-01-01	48.440
2001-01-01	46.540
2002-01-01	43.630
2003-01-01	40.940
2004-01-01	41.720
2005-01-01	42.910
2006-01-01	44.230
2007-01-01	46.200