Year	Number
1971	9.42424
1972	11.19231
1973	12.08889
1974	16.05882
1975	13.28671
1976	13.84314
1981	7.42989
1982	7.07347
1983	7.72937
1984	8.45906
1985	8.35812
1986	9.33368
1987	7.99099
1991	11.56702
1992	7.69471
1993	11.1704
1994	11.06165
1999	29.37538
2000	29.37746
2001	29.39791
2008	18.31441
2009	19.89906
2010	17.76118
2011	17.25623
2017	29.48773