Year	Percent
1961	36.02524
1962	36.92835
1963	37.39793
1964	37.85038
1965	38.76341
1966	38.77422
1967	38.77693
1968	38.77873
1969	38.78324
1970	38.78324
1971	40.60748
1972	40.6201
1973	40.63452
1974	40.64804
1975	40.66246
1976	40.67598
1977	40.84272
1978	40.79405
1979	40.80847
1980	40.82199
1981	40.83641
1982	40.84993
1983	40.86435
1984	40.87968
1985	40.8968
1986	40.91483
1987	40.92023
1988	40.81388
1989	40.72375
1990	40.63362
1991	40.45426
1992	40.54349
1993	40.47138
1994	40.43713
1995	40.11987
1996	40.48671
1997	40.63272
1998	41.04822
1999	41.16088
2000	40.43173
2001	37.62506
2002	37.50068
2003	37.90086
2004	38.2073
2005	38.35692
2006	38.01172
2007	38.24786
2008	38.40829
2009	38.3416
2010	38.30825
2011	37.60342
2012	38.41154
2013	40.39261
2014	40.37855
2015	40.36449
2016	40.35043
2017	39.19513
2018	39.70077
2019	39.97657
2020	39.70462
2021	38.50203