Year	Percent
1971	21.94932
1972	30.03203
1973	35.85947
1974	43.33543
1975	35.67266
1976	29.69483
1977	16.72099
1978	16.21959
1979	19.54404
1980	19.81533
1981	16.90049
1982	18.31275
1983	15.71405
1984	11.32097
1985	6.01133
1986	6.36272
1987	9.03284
1988	14.35057
1989	14.86402
1990	11.27022
1991	10.49594
1992	10.81335
1993	10.78878
1994	16.06396
1995	15.61138
1996	17.38005
1997	18.17606
1998	17.63454
1999	19.5147
2000	16.48083
2001	15.86825
2002	15.26661
2003	16.76622
2004	20.61114
2005	25.37873
2006	37.02958
2007	39.17308
2008	42.27538
2009	49.70704
2010	43.45106
2011	34.38463
2012	34.51038
2013	29.42173
2014	28.43181
2015	27.86228
2016	21.83197