Year	Number
1971	23.28814
1972	15.26768
1973	22.7946
1974	23.03236
1975	24.09297
1976	22.65483
1977	28.96576
1978	24.26555
1979	16.59967
1980	17.02457
1981	15.91959
1982	16.47691
1983	17.80691
1984	17.65817
1985	17.61463
1986	19.24076
1987	17.46766
1988	17.71423
1989	18.95033
1999	23.02476
2000	23.92029
2002	21.56908
2004	22.0955
2005	22.09495