Year	Number
1972	17.6258
1973	12.33597
1974	10.64914
1975	10.38
1976	14.36931
1977	7.49013
1978	7.71564
1979	7.93116
1980	8.26707
1981	7.89556
1982	8.06683
1983	8.30134
1984	8.05686
1985	8.311
1986	8.00809
1987	7.89596
1988	11.71356
1989	13.96206
1990	14.8303
1991	15.06264
1992	15.40113
1993	16.37687
1994	16.99399
1995	17.2749
1996	17.37911
1997	18.33865
1998	18.86603
1999	18.77739
2000	19.21494
2001	20.14845
2002	19.8591
2003	21.04939
2004	20.56551
2005	19.61694
2006	20.0581
2007	19.01529
2008	19.17729
2009	18.4081
2010	17.44734
2011	16.79334
2012	15.94788