Year	% of total
1970	26.07761795581271
1971	25.97471445285547
1972	25.676077625311862
1973	26.544904337808507
1974	24.644910963957482
1975	25.80168200653439
1976	27.300260877272457
1977	26.756680285616092
1978	27.275119699784085
1979	28.310945884786964
1980	26.309915193357288
1981	27.879575523176776
1982	27.7953886729088
1983	27.706920876261098
1984	27.624029667339588
1985	27.441113200451294
1986	27.532389360751004
1987	27.418138352071566
1988	26.282140113315872
1989	25.754424402405046
1990	34.92231638418079
1991	34.644532659689645
1992	34.55777460770328
1993	34.652406417112296
1994	33.118425517475394
1995	31.197301854974707
1996	29.432855280312907
1997	28.29346092503987
1998	29.008403361344538
1999	36.59158521036974
2000	33.11613645074741
2001	37.46713409290096
2002	39.26189417518897
2003	39.54219030520647
2004	39.58333333333333
2005	39.78300180831826
2006	39.38979963570127
2007	41.1371237458194
2008	40.25157232704403