Year	% of total
1970	3.2814916672437744
1971	3.316441984104495
1972	3.474264726009223
1973	3.569696833479693
1974	4.124304994319961
1975	3.9600733930131526
1976	3.890238123274963
1977	3.593409158996291
1978	3.9828102833657195
1979	3.9008049399827827
1980	3.690837073836721
1981	4.143410711732262
1982	3.7921214241273793
1983	4.166427367812582
1984	4.312409330794006
1985	4.4127324432926445
1986	4.0806569464721765
1987	3.9140971141948526
1988	4.086161663220342
1989	3.8485444765091117
1990	18.872017353579178
1991	19.791666666666664
1992	21.095334685598377
1993	22.027290448343077
1994	22.916666666666664
1995	24.20856610800745
1996	24.16225749559083
1997	25.622775800711743
1998	27.01252236135957
1999	26.28951747088186
2000	25.152439024390244
2001	27.608346709470304
2002	29.915966386554622
2003	32.801418439716315
2004	30.573248407643312
2005	30.709876543209873
2006	30.37593984962406
2007	32.49211356466877
2008	31.626506024096386