Year	Percent
1961	43.92582
1962	43.85246
1963	43.49322
1964	43.27059
1965	43.04797
1966	42.8987
1967	42.72414
1968	42.65584
1969	42.68873
1970	42.3472
1971	42.13216
1972	42.06638
1973	41.83617
1974	41.67932
1975	41.58571
1976	41.55535
1977	41.52499
1978	41.61354
1979	41.96263
1980	41.82673
1981	41.71622
1982	41.59355
1983	41.47125
1984	41.3485
1985	41.21171
1986	41.10409
1987	40.98243
1988	40.86113
1989	40.74019
1990	40.60359
1991	40.49938
1992	40.3795
1993	40.25999
1994	40.14082
1995	40.02201
1996	39.92847
1997	39.85151
1998	39.77492
1999	39.69376
2000	39.61727
2001	39.54077
2002	39.4656
2003	39.38948
2004	39.31192
2005	39.23488
2006	39.15905
2007	39.08308
2008	38.99911
2009	38.91545
2010	38.83284
2011	38.75021
2012	38.66766
2013	38.58538
2014	38.50281
2015	38.42057
2016	38.33866
2017	38.25988
2018	38.18241
2019	38.10503
2020	38.02711
2021	37.94969