Year	% of total
1960	25.16536007108015
1961	26.444836634356
1962	28.184871276754976
1963	28.78863214089446
1964	29.03716614548624
1965	29.209732260390346
1966	29.586147566489114
1967	30.850965132013116
1968	31.994878422118134
1969	32.911526922856844
1970	34.094823298266554
1971	34.234482273824305
1972	35.33349383975429
1973	36.432074932647666
1974	37.609004806369406
1975	37.82793797323294
1976	37.324273719662266
1977	37.39247183257377
1978	38.78268853498557
1979	38.66470867611816
1980	38.086089522262924
1981	39.29421438230107
1982	38.75996524052652
1983	38.234026639705135
1984	37.06969304342648
1985	34.705225489720085
1986	34.64686760668214
1987	30.653679682562984
1988	29.621849324541966
1989	29.878339955095434
1990	51.45033720269577
1991	52.15793861082834
1992	29.083223248879293
1993	29.3911119832692
1994	24.93829192681369
1995	24.223430123330562
1996	23.129120100626963
1997	23.514837287850547
1998	23.29103770858154
1999	22.236200460117434
2000	22.389503054716346
2001	22.442178755207877
2002	21.706470852438795
2003	21.63669482784672
2004	21.309483612755194
2005	21.664727504327665
2006	21.78166959102944
2007	21.326760120891482
2008	22.942334515293155
2009	24.00324310947919
2010	21.700284810126583
2011	23.900883630805524
2012	24.077295933671692
2013	22.827471274984298
2014	24.50873952926826
2015	23.221374676571234
2016	25.56288719054151