Year	Number
1970	24.0339
1971	23.72075
1972	23.50184
1973	23.38419
1974	26.78439
1975	26.34827
1976	25.49151
1977	24.68662
1978	26.48416
1979	25.32676
1980	25.14808
1981	24.98121
1982	25.53461
1983	25.14604
1984	24.42839
1985	25.87968
1986	21.39697
1990	19.37241
1991	20.51926
1992	21.41365
1993	24.29529
1994	24.06245
1997	23.45263
1999	19.24884
2010	19.91627
2011	19.52728
2012	19.13812
2013	20.59775
2014	20.31899
2015	25.73093
2016	25.15321
2017	25.77788
2018	25.41046