Year	% of total
1960	42.99621530934146
1961	43.4796596982929
1962	44.342495941884245
1963	42.17594901827946
1964	42.860160380652026
1965	41.58646905401846
1966	39.32313496319973
1967	40.65667945120768
1968	39.85275805520537
1969	38.221009839151
1970	37.53361970519006
1971	42.624980664841914
1972	40.33388805997186
1973	38.80476139375361
1974	38.27753868999367
1975	37.67234143487583
1976	39.649473201766064
1977	38.676274786804285
1978	38.934765199381324
1979	38.972202404567106
1980	40.247145952214154
1981	39.024741671151794
1982	41.17184235974759
1983	41.21461744374221
1984	40.12889168055413
1985	39.039946667223425
1986	38.07409715505503
1987	37.10244034308301
1988	36.257795561048454
1989	36.69387026685794
1990	36.4777237606432
1991	35.745153824737244
1992	34.79782006658231
1993	33.85021941626087
1994	33.77028977337761
1995	33.50384337956323
1996	33.06217710229981
1997	31.970331245585726
1998	31.701388847827484
1999	30.81466013543842
2000	31.616520108976747
2001	30.48931197451834
2002	31.018399955972185
2003	31.436850222689177
2004	30.16346661393961
2005	29.114176315082336
2006	28.88737639280558
2007	29.24049237577669
2008	26.64408158236088
2009	25.829871653803423
2010	24.843948826986317
2011	26.0095489452299
2012	26.58530607299045
2013	26.311927611279064
2014	25.59534285041492
2015	25.64397339096439