Year	Percent
1971	4.7894
1972	8.30386
1973	21.6587
1974	24.22993
1975	10.73489
1976	20.87346
1977	32.9225
1978	43.92563
1979	54.90201
1980	34.02606
1981	13.98018
1982	10.28607
1983	6.16
1984	5.28019
1985	9.19262
1986	8.40304
1987	6.35865
1988	8.73923
1989	4.90838
1990	9.95883
1991	11.36329
1992	16.68526
1993	23.96273
1994	21.31096
1995	16.17794
1996	17.74162
1997	17.48487
1998	17.56534
1999	17.34547
2000	16.76105
2001	9.53525
2002	7.07417
2003	8.66193
2004	11.70217
2005	21.47109
2006	26.92731
2007	38.19749
2008	35.74921
2009	35.90781
2010	41.22476
2011	33.16329
2012	31.65542
2013	20.83251
2014	21.59237
2015	14.71291
2016	20.16619