Year	% of total
1970	32.08812816804361
1971	31.43027423673268
1972	30.12504385896715
1973	31.37310321171386
1974	33.01587526391157
1975	33.4518160530174
1976	34.58953198513438
1977	33.982199106932356
1978	34.027627430212014
1979	33.61374133234114
1980	33.751373544342584
1981	34.45983024830242
1982	34.208407375467885
1983	35.222952556098406
1984	36.56915238304694
1985	38.137924783431465
1986	37.74670841346079
1987	38.609390069343455
1988	38.933116696276194
1989	39.243073126496796
1990	27.782225780624497
1991	27.124773960217
1992	26.75074676402257
1993	26.646058732612055
1994	26.54124457308249
1995	26.548431105047747
1996	26.447131463853875
1997	26.101613291596436
1998	26.743366987555767
1999	25.967812092214004
2000	25.811117999586692
2001	26.12929962702031
2002	25.639476334340383
2003	25.69541725035021
2004	25.663366336633665
2005	25.79881656804734
2006	25.848513902205177
2007	25.82867783985102
2008	26.06392694063927