Year	Number
1970	11.43152
1971	10.68631
1973	9.54794
1974	9.96104
1980	9.9614
1981	10.50566
1982	10.66245
1983	11.04273
1984	12.11923
1985	11.54133
1986	11.55831
1987	10.61927
1988	11.1182
1989	11.68821
1990	9.86586
1991	11.34337
1992	12.08788
1993	13.11113
1995	15.59389
1996	15.83902
2013	17.15687
2014	17.406
2015	16.67066
2016	17.17207
2017	15.9588