Year	Percent
1972	17.87152
1973	17.04836
1974	18.08918
1975	19.90695
1976	20.33336
1977	20.56741
1978	20.43797
1979	19.80212
1980	20.44646
1981	21.49831
1982	21.62158
1983	21.74978
1984	21.04863
1985	22.54901
1986	22.61729
1987	23.26702
1988	23.17454
1989	22.68629
1990	22.47248
1991	22.37112
1992	20.68109
1993	20.01926
1994	20.04522
1995	21.21431
1996	21.92915
1997	22.43094
1998	22.27201
1999	22.48754
2000	23.08738
2001	24.8325
2002	23.53799
2003	24.33415
2004	24.36135
2005	24.86867
2006	24.62723
2007	24.1423
2008	24.29616
2009	22.09327
2010	20.56542
2011	20.36926
2012	21.23624
2013	22.05965
2014	22.02765
2015	22.04281
2016	22.28929