Year	Percent
1972	10.67248
1973	10.8274
1974	11.12131
1975	11.08541
1976	11.66172
1977	13.09374
1978	12.68204
1979	12.80924
1980	13.63016
1981	12.39759
2003	13.74647
2004	14.49586
2005	14.53495
2006	15.23836
2007	16.385
2008	16.13052
2009	14.16197
2010	14.4251
2011	14.78798
2012	14.74747
2013	15.06324
2014	16.54264
2015	17.34447