Year	Percent
1960	35.34741
1961	34.0731
1962	37.57419
1963	38.44981
1964	36.83208
1965	32.41864
1966	34.70786
1967	33.65743
1968	31.7057
1969	30.89757
1970	30.16973
1971	28.16229
1972	32.21094
1973	31.8775
1974	31.29914
1975	30.17298
1976	33.32692
1977	37.00683
1978	32.06422
1979	30.18625
1980	27.79076
1981	27.87345
1982	28.9666
1983	29.86876
1984	29.5099
1985	28.60623
1986	28.77758
1987	27.17165
1988	25.5402
1989	25.96381
1990	25.31413
1991	24.32015
1992	24.78129
1993	26.80801
1994	28.11536
1995	26.34962
1996	27.49252
1997	27.69394
1998	27.74491
1999	28.74408
2000	28.72178
2001	27.84926
2002	25.85397
2003	25.80444
2004	24.92904
2005	24.23627
2006	20.51969
2007	20.58666
2008	22.19634
2009	16.25498
2010	17.56776
2011	18.89471
2012	18.82973
2013	18.61655
2014	18.34784
2015	19.46961
2016	20.03452
2017	20.89364
2018	20.31491
2019	20.86116
2020	22.70273
2021	21.47708
2022	21.16572