On the prevalence of trends in primary commodity prices

This paper applies new time series procedures to examine the Prebisch–Singer hypothesis of a secular deterioration in relative primary commodity prices. Specifically, we allow for (up to) two structural breaks in 24 price series, covering the 1900–98 period. For the majority of commodities, it is shown that the trend is not well represented by a single downward slope, but instead by a shifting trend that often changes sign over the sample period. Unlike some recent work that has also allowed for structural breaks, these results provide much less support for the Prebisch–Singer hypothesis.