Year	Number
1971	27.58111
1972	28.20275
1973	27.71645
1974	26.51934
1978	22.85246
1979	22.77318
1980	23.22449
1981	19.77134
1982	19.63647
1983	18.51562
1984	19.21565
1986	21.11722
1987	21.03886
1988	22.74969
1989	23.41361
1990	23.26197
1991	23.89033
1992	23.37143
1993	24.04789
1994	23.74015
1995	23.32419
1997	21.75622
2012	17.94572
2013	20.13252
2014	19.48105
2015	18.45287
2017	17.34797