Year	Percent
1972	18.67534
1973	17.84425
1974	18.87345
1975	17.72182
1976	18.83999
1977	18.24079
1978	18.25724
1979	18.83169
1980	19.29192
1981	19.36757
1982	19.60021
1983	19.44421
1984	19.56741
1985	19.65146
1986	19.65977
1987	19.87065
1988	19.21245
1989	18.906
1990	18.73425
1991	18.91823
1992	18.46669
1993	18.38408
1994	19.08412
1995	19.40911
1996	20.32412
1997	21.03812
1998	22.98187
1999	23.5791
2000	23.35314
2001	23.34729
2002	22.54241
2003	22.09024
2004	22.14576
2005	22.29322
2006	22.56964
2007	22.14654
2008	22.03425
2009	20.7084
2010	21.95196
2011	21.83272
2012	22.55348
2013	23.23331
2014	23.1796
2015	23.1817
2016	23.14513