An Empirical Study of Price Correlations: 2. The Decrease in Price Correlation with Distance and the Concept of Correlation Length
The dependence of the correlation between wheat price fluctuations on different markets with respect to the distance between those markets is investigated. It is shown that the decrease in the correlation is exponential and is governed by a characteristic distance which is called the correlation length for wheat prices. This is a measure of the level of market integration in a given area. The magnitude of the correlation length is compared for different cereals: wheat, rye, and oats, and the evolution of the correlation length during the 19th century is studied. In particular, it is observed that subsistence crises are characterised by a collective behaviour of the economy which results in a sudden peak in the correlation length. Last, the part played by the spatial correlation between precipitations is investigated. It appears to be rather small; consequently, the price-correlation length is primarily the result of economic factors.
Interregional Correlations in Wheat Yields and Outputs
Variations in world wheat production, region by region, display less regularity and uniformity than is sometimes assumed or asserted. Variations in wheat yields in remote regions of the several continents are very little related among themselves. The correlation between yields is not close even in far-distant regions of the same continents, as, for instance, in the wheat regions of North America. Fairly close correlations among regional wheat yields and outputs exist only for relatively limited areas, the weather developments within which are controlled by similar meteorological factors.
Spatial variation : Stochastic models and their application to some problems in forest surveys and other sampling investigations
Spatial variation : Stochastic models and their application to some problems in forest surveys and other sampling investigations