Year	% of total
1960	79.94778311343185
1961	78.64515569433603
1962	78.76899262699092
1963	74.80464470897539
1964	76.5693814500756
1965	74.33131107856909
1966	79.57527240382477
1967	79.67268710017214
1968	81.10962118672478
1969	81.0270353235249
1970	81.4726311739333
1971	77.67178810443963
1972	78.67513448356512
1973	81.75932682305817
1974	80.41894745916125
1975	79.37862705391484
1976	79.64577442664154
1977	83.54164898711312
1978	83.34732032543069
1979	82.5833213816842
1980	86.00604826007519
1981	85.832811521603
1982	86.484441592522
1983	88.0938616526247
1984	88.76542545558904
1985	88.20157111816815
1986	88.06610621021902
1987	89.3045322871285
1988	89.1325726351107
1989	89.62143566173971
1990	90.34396935581093
1991	89.40179894720703
1992	89.93313474856404
1993	89.45085642872895
1994	89.80552614420138
1995	90.37585718005845
1996	90.77027217599775
1997	90.41232427340785
1998	91.5659499843605
1999	91.45594641182161
2000	91.61838142797241
2001	91.90154504715403
2002	92.13908117759854
2003	91.5593011342515
2004	91.81334980916951
2005	91.19629336054338
2006	90.70069222737371
2007	91.35192753283205
2008	91.88474244362804
2009	92.50206574094601
2010	91.38812037157977
2011	89.57334772180366
2012	89.40734663969289
2013	86.73589161168331
2014	85.09328779041665
2015	86.36215890532591