Year	Percent
1972	17.24936
1973	17.79144
1974	17.43703
1975	18.33534
1976	18.22552
1977	19.08682
1978	19.14721
1979	19.29994
1980	19.1759
1981	18.59774
1982	19.8572
1983	19.75459
1984	20.95895
1985	22.70725
1986	21.85509
1987	21.69525
1988	22.7654
1989	25.30205
1990	23.11194
1991	22.90377
1992	20.62165
1993	21.77523
1994	21.53464
1995	22.42024
1996	23.2065
1997	23.53246
1998	24.38843
1999	24.13044
2000	23.34369
2001	24.18558
2002	23.27842
2003	23.03755
2004	24.2821
2005	25.7433
2006	27.26987
2007	27.59604
2008	26.81322
2009	24.3968
2010	25.0415
2011	25.17982
2012	25.58813
2013	26.04391
2014	26.54119
2015	27.33622
2016	27.09698