Year	Percent
1977	14.22071
1978	15.22271
1979	16.77566
1980	16.89195
1981	16.68443
1982	16.5335
1983	16.51801
1984	15.91464
1985	15.93451
1986	16.78127
1987	17.19503
1988	17.29322
1989	17.78814
1990	16.39328
1991	17.07205
1992	17.93752
1993	18.37823
1994	18.92852
1995	17.96073
1996	17.618
1997	19.02868
1998	19.24937
1999	17.84818
2000	17.1002
2001	16.84424
2002	15.59145
2003	16.20736
2004	16.80253
2005	16.38434
2006	16.46139
2007	18.74371
2008	16.01612
2009	16.19634
2010	16.48114
2011	15.65333
2012	15.15551
2013	15.33535
2014	14.80962
2015	15.30867
2016	14.76534
2017	14.99365