Year	Percent
1960	4.67911
1961	4.01675
1962	3.42782
1963	4.01004
1964	7.5436
1965	7.65656
1966	7.81752
1967	7.92878
1968	8.07103
1969	8.186
1970	8.33412
1971	8.49853
1972	8.65021
1973	8.21509
1974	6.29444
1975	6.15443
1976	5.99307
1977	5.88462
1978	5.88694
1979	5.99728
1980	6.19095
1981	6.34278
1982	6.46769
1983	6.71766
1984	7.22634
1985	7.43865
1986	7.67562
1987	7.80343
1988	7.70562
1989	7.3378
1990	6.84395
1991	6.32874
1992	5.91139
1993	5.47816
1994	4.89246
1995	4.86948
1996	4.86423
1997	4.83485
1998	4.84157
1999	4.87015
2000	4.91446
2001	4.96653
2002	5.00954
2003	4.95487
2004	4.66404
2005	4.62776
2006	4.58566
2007	4.54919
2008	4.51845
2009	4.48953
2010	4.46821
2011	4.44234
2012	4.41373
2013	4.36899
2014	4.31631
2015	4.25626
2016	4.19183
2017	4.12943