In September 2009, we reported that the price index of crude oil
had been likely evolving in sync with that of iron and steel,
but with a lag of two months. In order to present both indices
in a comparable form, the difference between a given index,
iPPI, and the overall PPI was normalized to the PPI:
(iPPI(t)-PPI(t))/PPI(t). The normalized differences represent
the evolution of the rate of deviation from the PPI over years.
Figure 1 depicts corresponding time histories of the normalized
deviations from the PPI. Simple visual inspection reveals the
following feature: the (normalized deviation from the PPI of
the) index of iron and steel lags by two months behind the
(normalized) index of crude oil. Figure 1. The deviation of the
iron and steel price index and the index of crude oil from the
PPI, normalized to the PPI. In order to reduce both deviations
to the same scale we additionally normalized the curves in
Figure 1 to their peak values between 2005 and 2009: This
scaling allows a direct comparison of corr