Year	% of total
1990	32.69500938748072
1991	32.5436174124333
1992	31.671928023836056
1993	31.39455559274277
1994	30.68227333445835
1995	30.464466761232575
1996	30.811814400993914
1997	30.994509887308077
1998	30.927652786479936
1999	31.05432241437348
2000	31.618476002409448
2001	32.4390169361401
2002	32.88643203431387
2003	33.99781876029167
2004	34.456591420825085
2005	34.83670367087319
2006	35.46991625066248
2007	36.059011011980324
2008	36.55155305007489