Year	% of total
1971	26.011777576789246
1972	30.491444075519166
1973	31.1053314170188
1974	26.345668714755504
1975	24.068027114858975
1976	23.533972442583885
1977	25.400109162844014
1978	27.408005232607795
1979	28.803040689282355
1980	29.233329775419165
1981	28.646841780369492
1982	30.575801868437658
1983	30.916228679050228
1984	26.805804788818527
1985	24.740671375884983
1986	24.50859955620694
1987	26.121178351167213
1988	24.74355180633285
1989	23.55703248549195
1990	24.113580733920674
1991	25.1337465664854
1992	24.797265346876184
1993	29.80516926045341
1994	31.69836899530138
1995	33.06375347680914
1996	37.551528113048015
1997	37.67683864446955
1998	38.92736154364206
1999	39.83703209689663
2000	43.02457759786992
2001	43.35644415158898
2002	44.587744468918736
2003	46.371876144257634
2004	45.796868228237194
2005	45.293833811317384
2006	43.43980101594961
2007	45.38813773537799
2008	44.86267170562512
2009	43.55871971095454
2010	43.08771553779471
2011	48.840184473511336
2012	47.31202305049012
2013	45.87418024187942
2014	50.54557397765795