Year	Number
1971	13.49564
1979	22.12917
1980	22.48398
1983	21.74063
1984	22.18517
1988	21.84386
1990	15.597
1991	16.06573
1995	12.80205
1997	14.25968
2008	19.86332
2012	14.54677
2015	16.59034