Year	% of total
1970	31.607830261939597
1971	30.990831033555306
1972	30.8397162139803
1973	32.28770555314883
1974	35.04638637984242
1975	33.93775364961616
1976	41.803849240470484
1977	41.48065441276086
1978	40.666147543875375
1979	39.84034900546944
1980	38.48719740709127
1981	37.19527327941982
1982	38.18827318449335
1983	38.8512394067247
1984	38.98239364023689
1985	38.6229494891072
1986	38.853586626965836
1987	39.30022191847996
1988	40.19659996555556
1989	39.58091809362935
1990	5.029940119760479
1991	4.761904761904762
1992	4.719101123595506
1993	4.684095860566448
1994	4.852320675105485
1995	4.713114754098361
1996	4.568023833167826
1997	4.4422507403751235
1998	4.505386875612145
1999	4.470359572400389
2000	4.536679536679537
2001	5.082872928176796
2002	5.706874189364462
2003	7.020280811232449
2004	6.3768115942028984
2005	6.016042780748663
2006	6.24203821656051
2007	6.125
2008	6.311881188118812