Year	Measure
1960	0.3567
1961	0.4178
1962	0.4402
1963	0.4271
1964	0.4822
1965	0.5161
1966	0.5017
1967	0.539
1968	0.5285
1969	0.4501
1970	0.4436
1971	0.5532
1972	0.5692
1973	0.6321
1974	0.6028
1975	0.605
1976	0.5736
1977	0.5578
1978	0.6003
1979	0.6332
1980	0.6091
1981	0.6176
1982	0.5689
1983	0.6563
1984	0.7007
1985	0.731
1986	0.6253
1987	0.7343
1988	0.7105
1989	0.7253
1990	0.7284
1991	0.631
1992	0.7365
1993	0.7345
1994	0.5781
1995	0.6634
1996	0.5028
1997	0.6706
1998	0.7285
1999	0.6963
2000	0.7626
2001	0.7658
2002	0.641
2003	0.5152
2004	0.5758
2005	0.6933
2006	0.5838
2007	0.6209
2008	0.643
2009	0.6081
2010	0.6087
2011	0.6035