Year	Percent
1971	5.3108
1972	6.46093
1973	6.55176
1974	6.47947
1975	6.86166
1976	7.51219
1977	8.40388
1978	10.24623
1979	10.67202
1980	13.72144
1981	14.63413
1982	16.92902
1983	18.33868
1984	19.97817
1985	19.62975
1986	21.67921
1987	22.82986
1989	14.93885
1990	16.34121
1991	17.3218
1992	18.13287
1993	16.08347
1995	13.45525
1996	13.8611
1997	17.87711
1998	18.85793
1999	19.44073
2000	18.38888
2001	19.36399
2002	21.08161
2003	20.46479
2004	26.62847
2005	29.40302
2006	32.19127
2007	39.06159
2008	37.64928
2009	39.86164
2010	39.72299
2011	44.21907
2012	47.81985
2013	47.91381
2014	57.86876
2016	71.62127