Year	Number
1971	46.69999
1972	40.93971
1975	39.53064
1977	37.16503
1979	43.83249
1980	41.37766
1981	41.43476
1983	33.78129
1984	34.29697
1985	34.59407
1986	35.24658
1987	36.18559
1988	33.77801
1989	33.08585
1990	33.64659
2003	29.65919
2004	27.53374
2011	23.39354
2012	22.85664
2013	21.67349
2014	22.08221
2015	21.97603
2016	22.64723
2017	22.10634
2018	24.79434