Year	% of total
1971	71.64412012239806
1972	67.59337261286701
1973	68.15555511200618
1974	74.06841271173926
1975	69.1717037722539
1976	67.80538348935717
1977	63.36272628543148
1978	57.02275927602428
1979	59.58091602293377
1980	58.40116513717072
1981	57.207742692751275
1982	55.3641491152422
1983	43.73918451167679
1984	42.670208016051944
1985	49.64899429297516
1986	52.43658546574467
1987	49.086137668996805
1988	51.86227332721101
1989	52.30439175016583
1990	51.96761648237068
1991	56.31523700632323
1992	55.09624540687543
1993	53.4437496443822
1994	50.723459071398466
1995	51.11545377673296
1996	50.53728923453272
1997	50.30787782914228
1998	44.98996982304513
1999	46.4208020793176
2000	49.46490821988891
2001	47.95724796091969
2002	42.640957737267726
2003	42.044854521911205
2004	41.661162187516496
2005	40.13915848413265
2006	35.885802630707744
2007	33.07238912821389
2008	37.9426038752037
2009	37.380788973207785
2010	34.53115241079161
2011	33.924500262405125
2012	31.743730367191336
2013	30.79267012461009
2014	30.496456825570164
2015	27.11430243751754