Date	First	Second	Third	Fourth
1917	14.3	2.8	11.7	11.2
1918	11.5	1.3	11.6	11.2
1919	13.2	1.1	9.8	9.9	
1920	12.1	1.2	8.3	9.6	
1921	13.4	2.1	8.4	10.6
1922	14.2	2	9.8	11.7
1923	13.4	1.9	9.1	10.9
1924	14.5	2.3	10.4	11.1
1925	15.8	3.1	14.2	12.2
1926	15.2	4.5	14	12.3	
1927	15.6	4.6	14.7	13.3
1928	17.6	5.2	17.5	14	
1929	14.2	2.9	14.3	12.2
1930	14.4	3	12	12.7
1931	14.5	3.1	11.4	11.6
1932	14.8	3	11.2	12.8	
1933	14.5	3.3	10.7	14	
1934	13.8	3.6	11.5	14.4
1935	14.1	4	11.8	13.9	
1936	15.7	4.4	13.7	16	
1937	15.5	4.3	12.7	14.5
1938	14.9	4.3	11.4	15.9
1939	16.1	5.1	11.7	15.7
1940	16.3	5.6	11.8	16.3
1941	15.9	5.9	12.2	17.2
1942	13.2	6.1	11.4	13.1
1943	11.7	5.2	9.2	12.9
1944	13.6	6.4	11	13.7	
1945	12	4.7	11.2	11.8	
1946	13.6	4.4	11.7	13.
1947	12.2	4	10	13.5
1948	12.1	4.4	11.4	12.3
1949	11.9	4	10.4	12.3	
1950	13	4.2	13.9	13.1	
1951	11.4	3.4	11.5	11.2
1952	10.6	4.5	10.6	10.2
1953	9.9	4.1	8.7	10.4
1954	10.9	4.3	9.8	12.7
1955	11.2	3.4	10.5	11.4
1956	10.6	3.4	10.4	11.5
1957	9.7	4.1	10	10.2	
1958	10.1	4.4	9.9	11	9
1959	10.5	4.1	10.9	11.6
1960	9.8	4.7	10.7	10.7
1961	9.3	5.4	9.9	10.6
1962	9.5	4.6	9.7	10.9
1963	10	4.6	9.4	11
1964	10.2	5.6	10.1	11.8
1965	10.3	5.9	10.7	12	
1966	10.3	5	9.3	10.9
1967	10.1	5.2	10.2	10.7
1968	10.3	5.1	10.3	11.7
1969	9.7	5.2	9.9	11
1970	9.1	5	8.8	9.7
1971	9.7	5.3	9.1	10.2
1972	9.8	5.2	9.1	10.4
1973	9.7	5.5	8.8	10.6
1974	8.8	8.4	7.8	9.7	
1975	9.7	4.8	8.2	10.3
1976	9.3	4.3	8.2	9.9