Year	% of total
1971	35.2715510693812
1972	35.66939036623533
1973	37.13289772618842
1974	38.325881009341785
1975	39.10467773701631
1976	40.2842850153386
1977	41.74999469020272
1978	41.82617974400647
1979	43.44926410277807
1980	43.92471806929627
1981	45.47901278907177
1982	47.15197215132146
1983	46.97917735618499
1984	47.77177410147177
1985	49.363241977857044
1986	50.35612604382778
1987	51.39400155679818
1988	51.997007196771094
1989	53.39515940851315
1990	64.7429436475241
1991	64.52749473462268
1992	63.73793567089745
1993	63.57651343145947
1994	62.93406425359976
1995	64.50762623822978
1996	64.19249299755703
1997	64.68931888657823
1998	64.51150451455005
1999	65.53583173649514
2000	65.22496678035378
2001	65.47533942659199
2002	65.95891953025124
2003	66.19978301510079
2004	66.83786252558505
2005	67.29122947354696
2006	67.5027755801107
2007	68.01540112430698
2008	68.60503422137025
2009	69.09892738932915
2010	69.57000558330853
2011	69.27275188229015
2012	69.60530711251363
2013	69.42923396597227
2014	69.96332404229112