Year	Number
1987	21.83091
1988	22.48256
1989	22.28738
1990	19.10929
1991	19.91687
1992	20.14284
1993	21.16658
1994	21.86205
1995	22.34247
2011	17.25639
2012	17.28218
2016	17.42213
2017	17.44801
2018	17.52875