Year	% of total
1970	7.754958096673303
1971	7.901533417820731
1972	7.75313009461533
1973	8.092359722566853
1974	8.896199477326265
1975	7.981243726603761
1976	8.341568085956867
1977	7.759730997191521
1978	7.528372305404591
1979	8.008405525331948
1980	8.537593907339843
1981	8.451922224684122
1982	8.496639671984388
1983	9.243118501006785
1984	9.32202260406175
1985	9.064040553182204
1986	9.105411134646364
1987	8.817732734909022
1988	8.619811803660195
1989	8.759041434057337
1990	2.8457598178713717
1991	3.31421287444232
1992	3.744798890429958
1993	3.56687898089172
1994	3.4278959810874707
1995	3.454231433506045
1996	3.545301069217783
1997	3.5852178709321567
1998	3.7321624588364433
1999	3.848238482384824
2000	3.9142091152815013
2001	3.9915966386554618
2002	4.091144484722942
2003	4.260780287474333
2004	4.363267376966007
2005	4.445554445554445
2006	4.838709677419355
2007	5.172413793103448
2008	5.373455131649651