Year	Number
1971	35.67778
1972	30.5614
1973	37.77184
1974	37.22271
1975	37.0757
1976	36.43284
1979	39.44413
1980	42.29722
1981	40.19332
1982	41.07826
1983	48.30496
1984	44.04637
1985	44.09589
1987	43.98055
1988	44.03664
1989	43.87206
1990	44.13221
1991	42.73046
1992	43.23927
1993	42.84174
1994	41.93774
1995	39.75482
1996	36.04279
1997	33.66423
1998	38.76771
1999	39.5383
2004	34.54823
2006	33.63267
2007	35.48341
2008	34.0344
2009	34.14014
2011	35.23512
2012	34.93245
2013	34.21598
2014	33.23979
2015	33.02204
2016	31.09517
2017	30.42105
2018	29.37453