Year	% of total
1960	27.75832822761205
1961	27.027019909675783
1962	26.927823322034616
1963	24.84711592596971
1964	24.847055633199528
1965	24.809884596808125
1966	23.871651219983992
1967	24.620307853601986
1968	22.6874807196383
1969	23.391389729072195
1970	22.279967368440026
1971	22.11775240272874
1972	21.57492079304918
1973	20.571104269710077
1974	22.96313552793093
1975	22.085946793484176
1976	20.485644582002706
1977	17.32795978089035
1978	19.489927199812325
1979	19.366363372035888
1980	18.915724036754007
1981	18.713831643687463
1982	20.619188713111882
1983	21.044139340984515
1984	20.344194705964096
1985	19.066580804240427
1986	19.43846361129625
1987	17.204945053931613
1988	15.329858822871135
1989	15.088939785173123
1990	15.460589398728427
1991	15.844159597345028
1992	15.050871141415323
1993	15.46154490193825
1994	14.782412392882453
1995	15.778625189945483
1996	16.72130503201112
1997	16.101680559745372
1998	14.378261473971996
1999	14.002418879896194
2000	13.203342235524085
2001	11.773401610150408
2002	13.341452954804181
2003	13.26064859213482
2004	12.88452598904754
2005	12.96996264892279
2006	13.190632212344955
2007	12.458258022174492
2008	12.743185358116943
2009	13.487374088724799
2010	12.371632966920417
2011	14.047832476739568
2012	13.418583931111089
2013	13.375169727925263
2014	12.907708144800512
2015	12.710177825236846