Year	Percent
1972	12.65359
1973	10.81125
1974	11.00086
1975	11.55773
1976	11.22907
1977	11.67167
1978	12.49302
1979	13.80688
1980	17.96171
1981	15.11633
1982	14.79299
1983	11.89773
1984	13.04041
1985	14.96299
1986	13.38211
1987	9.97442
1988	9.66358
1989	7.92166
1990	10.7239
1991	10.92277
1992	11.92571
1993	12.05261
1994	12.97214
1995	13.68476
1996	14.19981
1997	14.39876
1998	14.2348
1999	12.99419
2000	12.60865
2001	12.89711
2002	12.48714
2003	13.41152
2004	13.66337
2005	14.10474
2006	15.66999
2007	16.40747
2008	16.51217
2009	14.45653
2010	15.46657
2011	15.9689
2012	16.54669
2013	16.42956
2014	16.69571
2015	14.91015
2016	13.81709