Year	% of total
1971	15.311318951191897
1972	15.491215247691539
1973	16.02535140345433
1974	15.783346927836217
1975	15.366455616222208
1976	15.572214353049457
1977	16.08505851603815
1978	15.907291724227298
1979	15.494069824392579
1980	15.540540028219423
1981	15.168893150425129
1982	15.087390360727584
1983	14.177322440244925
1984	14.265050738627792
1985	13.968403415097693
1986	14.036994258669793
1987	14.198423462255017
1988	14.15262652379914
1989	14.028231622473742
1990	14.005779545673647
1991	13.296397323957983
1992	13.167507954829027
1993	12.932066170851002
1994	13.0486204499312
1995	13.943631341604519
1996	14.572670363091373
1997	15.049158801151151
1998	15.34313108887752
1999	16.581566404779895
2000	16.249467203339023
2001	15.64216284559543
2002	16.8288847992578
2003	16.794985795202045
2004	17.04783907934067
2005	17.317363860224386
2006	18.33743909856334
2007	19.023405165967826
2008	19.14419788853419
2009	19.19003397971758
2010	19.67985048927048
2011	19.835413382933762
2012	20.68542915930237
2013	21.049391108598208
2014	22.331944656180156