Year January December X.VALUE.
1  1959  315.42   315.43    -0.01
2  1960  316.27   316.03     0.24
3  1961  316.73   316.85    -0.12
4  1962  317.78   317.53     0.25
5  1963  318.58   318.20     0.38
6  1964  319.41   318.55     0.86
7  1965  319.27   319.25     0.02
8  1966  320.46   320.87    -0.41
9  1967  322.17   321.80     0.37
10 1968  322.40   322.74    -0.34
11 1969  323.83   323.95    -0.12
12 1970  324.89   324.96    -0.07
13 1971  326.01   325.85     0.16
14 1972  326.60   327.39    -0.79
15 1973  328.37   328.48    -0.11
16 1974  329.18   329.41    -0.23
17 1975  330.23   330.59    -0.36
18 1976  331.58   331.52     0.06
19 1977  332.75   333.68    -0.93
20 1978  334.80   334.78     0.02
21 1979  336.05   336.56    -0.51
22 1980  337.84   338.04    -0.20
23 1981  339.06   339.44    -0.38
24 1982  340.57   340.32     0.25
25 1983  341.20   342.82    -1.62
26 1984  343.52   344.04    -0.52
27 1985  344.79   345.38    -0.59
28 1986  346.11   346.72    -0.61
29 1987  347.84   348.78    -0.94
30 1988  350.25   351.18    -0.93
31 1989  352.60   352.37     0.23
32 1990  353.50   354.07    -0.57
33 1991  354.59   354.89    -0.30
34 1992  355.88   355.33     0.55
35 1993  356.63   356.78    -0.15
36 1994  358.34   359.05    -0.71
37 1995  359.98   360.74    -0.76
38 1996  362.09   362.38    -0.29
39 1997  363.23   364.34    -1.11