Year	% of total
1960	33.177387914230025
1961	33.445315416200074
1962	32.467532467532465
1963	35.686509123541725
1964	37.35440931780366
1965	37.47576997630842
1966	33.837986629964604
1967	32.34465928289844
1968	29.83407261376705
1969	31.409241399165104
1970	23.61153262518968
1971	24.073829927488465
1972	22.07897793263647
1973	22.81496062992126
1974	24.84560089095879
1975	29.233091217809644
1976	31.259613741240816
1977	29.36724662557541
1978	24.82458816351434
1979	26.429796968830427
1980	24.96969696969697
1981	28.16657027183343
1982	29.850221503410452
1983	34.5348913976365
1984	36.14628189472331
1985	39.21699140747913
1986	41.20930232558139
1987	41.83372811831995
1988	42.829405102205925
1989	42.372713791398915
1990	41.975075376884426
1991	40.32152334476392
1992	41.04619723714505
1993	41.17802919708029
1994	41.82118525021949
1995	39.84830275229358
1996	37.74670492991783
1997	40.181143744030564
1998	40.31469413520028
1999	38.57482608695652
2000	37.67545521914038
2001	37.930163544146566
2002	36.64722360248447
2003	35.05274396328078
2004	35.9391707561342
2005	34.62338597351643
2006	33.0612641509434
2007	33.44630236794172
2008	32.66372672044617
2009	35.144986278235166
2010	35.40970427038136
2011	36.82613483146067
2012	40.10852790610563
2013	38.030958885209714
2014	37.97757153127247
2015	32.53983972945155
2016	25.786936424831712