Year	Number
1961	1.7985611510791366
1962	1.9550342130987293
1963	2.1151968760169217
1964	2.2435897435897436
1965	2.302992518703242
1966	3.017048977061376
1967	3.86877127824203
1968	4.842236800999688
1969	6.191552062868369
1970	6.840390879478828
1971	7.9155672823219
1972	10.057020435069216
1973	9.665171419416854
1974	10.809040288241075
1975	11.595454545454546
1976	15.955351280367697
1977	20.071801566579634
1978	23.91653290529695
1979	28.14814814814815
1980	30.324820928059793
1981	35.943517329910144
1982	36.8147254073627
1983	44.990979381443296
1984	48.987854251012145
1985	49.39545884578997
1986	59.190444591904445
1987	64
1988	74.19786096256684
1989	80.23676422229529
1990	89.32033613445378
1991	91.2120093928212
1992	94.68582887700535
1993	88.68011908699967
1994	83.59041322314049
1995	100.12869336835193
1996	104.88281505728314
1997	106.63659793814433
1998	109.89717223650386
1999	113.33976213436195
2000	105.21746134020617
2001	108.26964856230032
2002	112.48334401024984
2003	116.53158063481885
2004	132.51831078851865
2005	139.44381836261186
2006	145.03331134564644