Year	% of total
1960	3.7721021611001966
1961	3.83155102379176
1962	3.6586688145727164
1963	3.594458367358432
1964	3.4573596676321414
1965	3.239944790178463
1966	3.7486575979953467
1967	3.611515277489088
1968	3.5044714226196825
1969	3.4777214173630626
1970	3.6293091608295565
1971	3.3965461588121366
1972	2.843293948944688
1973	2.6716973790266545
1974	2.8808176228673807
1975	2.734294612355774
1976	2.3562426212890104
1977	2.261181634112926
1978	2.2013759321622697
1979	2.1368834462762365
1980	2.1583439615422346
1981	1.9384869854823028
1982	1.9364667319305269
1983	1.8838592185843015
1984	1.932797434812621
1985	1.7625399891350275
1986	1.9497604489266525
1987	1.9693179755108627
1988	1.9906323185011712
1989	1.5455181903773267
1990	1.5383749243479852
1991	1.5106500830857545
1992	1.6019365153502076
1993	1.728366970807072
1994	1.5659700970534232
1995	1.5486762946360864
1996	1.7485526194872136
1997	1.867161006636271
1998	2.072105813013739
1999	2.2950377041908547
2000	2.4746148232391523
2001	2.772036161151037
2002	3.1697245723015723
2003	3.561573016438567
2004	3.8992213728586065
2005	4.167901900013475
2006	4.433343841711327
2007	4.833853521163317
2008	5.275462719319229
2009	6.9769538904399395
2010	8.651718863484987
2011	12.353316835635027
2012	16.935196334990483
2013	20.57525120784692
2014	22.341037552675864
2015	22.50587792386757