Year	Number
1961	51.6449603624009
1962	54.50453001132502
1963	57.40845070422536
1964	56.690140845070424
1965	57.68258426966292
1966	58.26330532212886
1967	59.235294117647065
1968	60.34173669467787
1969	62.02967525195968
1970	63.58622620380739
1971	65.68429890848026
1972	67.03177257525084
1973	66.0377358490566
1974	65.63415308096158
1975	66.53920220082532
1976	67.45479452054795
1977	69.81451172940535
1978	71.99130671013312
1979	74.38463619150663
1980	76.57058189655173
1981	79.13090128755364
1982	82.82126636387925
1983	85.1290236765097
1984	87.61526232114467
1985	88.25857519788917
1986	88.71747700394218
1987	89.51882845188285
1988	93.98186314921682
1989	95.04608294930875
1990	96.8229954614221
1991	102.04081632653062
1992	94.46254071661238
1993	92.37085186452275
1994	88.2768361581921
1995	95.87328053355564
1996	86.31319358816276
1997	82.70972823946435