1 1936       0.9
 2 1937       0.8
 3 1938       0.8
 4 1939       1.3
 5 1940       1.4
 6 1941       1.2
 7 1942       1.7
 8 1943       1.8
 9 1944       1.6
10 1945       1.5
11 1946       1.5
12 1947       2.0
13 1948       2.5
14 1949       2.7
15 1950       2.9
16 1951       2.5
17 1952       3.1
18 1953       2.4
19 1954       2.2
20 1955       2.9
21 1956       2.5
22 1957       2.6
23 1958       3.2
24 1959       3.8
25 1960       4.2
26 1961       3.9
27 1962       3.7
28 1963       3.3
29 1964       3.7
30 1965       3.9
31 1966       4.1
32 1967       3.8
33 1968       4.7
34 1969       4.4
35 1970       4.8
36 1971       4.8
37 1972       4.8