Year	Number
1971	7.49469
1972	7.16542
1973	6.92369
1974	7.42204
1975	8.06912
1976	8.66625
1977	9.27939
1978	9.95958
1979	10.24164
1980	10.67086
1981	10.80033
1982	10.82902
1983	10.56898
1984	10.35312
1985	9.4006
1986	9.24454
1987	9.16118
1988	8.68087
1989	9.02423
1990	9.74038
1991	9.98344
1992	9.42081
1993	7.87674
1994	8.68747
1996	9.69214
1999	12.05108
2000	12.67841
2001	12.36891
2003	12.98882
2005	13.84093
2006	14.98998
2011	24.78408
2012	25.19055
2013	26.02222