Year	% of total
1970	4.586120673641704
1971	4.652398857621256
1972	4.889657085467476
1973	5.078229139169358
1974	5.346446780666843
1975	5.360527063438323
1976	5.390687290618258
1977	5.736088371281635
1978	4.576100434963582
1979	4.228103724324041
1980	4.373521874848825
1981	4.216294841173478
1982	4.586600457809252
1983	4.729950751457204
1984	4.753272407007889
1985	5.311438810455133
1986	5.3598254628042
1987	5.115085096009094
1988	5.70159317414359
1989	5.815204304040689
1990	7.124681933842239
1991	7.408814589665654
1992	7.292048369366068
1993	7.932607932607932
1994	8.72613946240748
1995	8.982725527831095
1996	9.332833583208396
1997	9.433258762117823
1998	8.816210451475294
1999	8.831908831908832
2000	9.160028964518464
2001	9.432454036770583
2002	9.46372239747634
2003	10.526315789473683
2004	11.26126126126126
2005	11.491712707182321
2006	11.678832116788321
2007	13.558106169296988
2008	15.428354814253224