Year	Number
1972	11.55264
1973	11.3583
1974	10.07844
1975	9.14944
1976	11.29501
1977	12.21507
1978	12.19016
1979	11.23223
1980	10.88828
1982	10.73654
1983	13.34082
1984	11.26916
1985	11.69554
1986	11.71293
1987	13.68039
1988	14.78685
1989	15.95222
1990	16.03654
1991	16.13005
1992	17.05313
1993	17.29599
1994	13.69192
1995	13.99435
1996	14.12353
1997	14.98675
1998	14.78757
1999	14.73357
2000	14.74036
2001	14.06263
2002	15.2058
2003	14.24871
2004	13.21138
2005	16.04412
2006	15.38189
2007	15.35568
2008	12.7741
2009	14.18543
2010	15.38655