Year	Number
1971	27.30645
1972	23.68994
1973	19.63619
1974	17.17656
1975	14.75211
1976	16.3607
1977	15.67131
1978	16.04642
1979	16.23312
1980	16.25985
1981	16.33794
1982	21.48346
1983	21.77902
1984	24.01023
1985	24.1961
1986	24.84485
1987	24.35787
1988	24.96814
1989	18.34669
1990	18.08003
1991	18.28038
1992	17.63254
1993	17.10681
1994	17.02467
1995	16.99968
1996	16.53584
1997	16.07066
1998	15.85782
1999	16.01551
2000	16.14708
2001	15.94765
2002	15.27716
2003	15.21595
2004	15.00218
2005	15.23077
2006	15.47687
2007	17.19022
2009	15.60016
2010	16.83357
2011	17.03397
2012	18.18358
2013	16.06864
2014	18.93254
2015	23.61794
2016	24.52278