Year	Percent
1973	11.48521
1974	11.77853
1975	12.31294
1976	13.84242
1977	14.11138
1978	13.45565
1979	13.76633
1980	15.17936
1981	16.08978
1982	16.59308
1983	18.33617
1984	18.00886
1985	17.61418
1986	17.54953
1987	15.57289
1988	16.98506
1989	17.73738
1990	17.66676
1991	18.28934
1992	20.02429
1993	18.58479
1994	19.35183
1995	19.78973
1996	20.61202
1997	20.38898
1998	20.53205
1999	21.05743
2000	21.01215
2001	20.63182
2002	20.94157
2003	20.90847
2004	19.93299
2005	20.47417
2006	21.06591
2007	21.33124
2008	21.03196
2009	19.17956
2010	19.69832
2011	21.23463
2012	20.88258
2013	22.75065
2014	22.72343
2015	22.86071
2016	22.53094