Year	Number
1973	19.59516
1974	19.37954
1976	19.13312
1977	19.96334
1978	20.08084
1979	19.46536
1980	19.76362
1981	24.23845
1982	26.62452
1983	30.30987
1986	27.54642
1987	27.48683
1988	27.14925
1989	27.30541
1991	28.17122
1992	28.29355
1993	29.88175
1994	25.7173
1995	25.89752
1996	26.59266
1997	27.7267
1999	27.30865
2000	24.71045
2001	24.45705
2002	25.92409
2003	22.32449
2012	22.43191
2013	22.48353