Year	Percent
1970	10.82754
1971	10.57113
1972	10.01956
1973	9.47876
1974	8.27175
1975	8.28284
1976	8.76047
1977	9.44093
1978	8.72368
1979	8.05625
1980	7.40376
1981	7.25213
1982	6.76075
1983	7.23428
1984	6.75709
1985	6.86478
1986	7.33706
1987	7.41978
1988	7.96047
1989	8.50386
1990	8.07414
1991	7.65628
1992	6.91969
1993	6.59006
1994	6.46079
1995	6.48593
1996	6.43515
1997	6.31549
1998	6.42734
1999	6.0211
2000	6.29327
2001	6.73217
2002	6.6827
2003	6.86791
2004	6.43838
2005	6.01558
2006	5.75046
2007	4.84692
2008	4.49517
2009	3.79324
2010	3.6124
2011	3.22924
2012	3.04751
2013	2.94452
2014	2.84988
2015	2.786
2016	2.60052
2017	2.38471
2018	2.37048
2019	2.3573
2020	2.94524
2021	2.65507
2022	2.61945