Year	% of total
1960	37.451975850713495
1961	38.64562787639711
1962	39.804822043628015
1963	40.28268551236749
1964	41.85396115122547
1965	42.57499534190423
1966	42.81482772139217
1967	43.01066709122751
1968	41.871019691091426
1969	41.248727296613794
1970	41.03190352617921
1971	41.82549396747683
1972	41.22175454142668
1973	39.73337380789761
1974	42.465320797803855
1975	43.14545290182607
1976	43.70842862838079
1977	41.57245632065776
1978	39.526835356859195
1979	37.76323171872078
1980	39.10627028236786
1981	40.77946592149823
1982	41.449389375889716
1983	40.25852927194939
1984	36.34602344279764
1985	35.29189780746444
1986	34.809345862206584
1987	32.14594351688616
1988	31.653597587246878
1989	31.11461205198897
1990	38.26102299716156
1991	38.279688860795055
1992	38.529840463528856
1993	39.66868582114927
1994	36.93445477452429
1995	36.49990805930589
1996	35.88009358612344
1997	32.18566831246694
1998	34.530086527819705
1999	36.78151111111111
2000	35.25072907290729
2001	32.076021676761236
2002	33.35132385938669
2003	33.86508733186107
2004	33.00034632482166
2005	33.28278050307901
2006	32.867349909035774
2007	30.30864475321443
2008	29.252037601092322
2009	30.093810233482365
2010	31.88160774193548
2011	30.29697677188803
2012	30.20014315428851
2013	31.292480211081795
2014	29.984054054054056
2015	28.018093278463645
2016	28.99991847062131