Year	Percent
1964	3.65625
1965	3.88873
1966	4.16343
1967	4.84293
1968	4.84437
1969	4.64403
1970	4.33621
1971	4.00074
1972	5.09034
1973	3.81529
1976	12.12491
1977	4.73228
1978	8.4896
1979	10.07175
1980	12.35714
1981	9.58333
1982	9.28645
1983	13.45562
1984	10.96873
1985	6.28698
1986	5.26384
1987	1.12185
1988	1.18658
1990	7.55195
1991	5.15489
1992	7.984
1993	6.01128
1994	6.99771
1995	6.71193
1996	5.66185
1997	4.30515
1998	4.02325
1999	4.77044
2000	5.38816
2001	5.4309
2002	4.73815
2003	4.5977
2004	4.51423
2005	4.47895
2006	4.57609
2007	4.63237
2008	4.00127
2009	4.02004
2010	4.12652
2011	4.05866
2012	3.9846
2013	4.09931
2014	4.62453
2015	4.41213
2016	5.03367
2017	4.51385