Year	Percent
1960	2.02429
1961	3.92157
1962	7.02341
1963	8.63095
1964	9.7035
1965	11.47959
1966	10.12346
1967	11.57571
1968	12.30349
1969	11.67233
1970	10.1833
1971	9.14077
1972	11.25402
1973	14.26873
1974	12.68293
1975	18.08318
1976	34.26791
1977	23.79536
1978	25.02157
1979	32.74662
1980	37.04276
1981	37.59911
2007	22.40605
2008	25.74935
2009	27.71041
2010	28.40673
2011	22.66323
2012	32.0387
2013	29.66372
2014	31.42685
2015	28.77755
2016	28.30103