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The natural rubber is a non-wood product obtained of the coagulation of some lattices of forest species, being Hevea brasiliensis the main one. Native from the Amazon Region, this species was already known by the Indians before the discovery of America. The natural rubber became a product globally valued due to its multiple applications in the economy, being its almost perfect substitute the synthetic rubber derived from the petroleum. Similarly to what happens with other countless products the forecast of future prices of the natural rubber has been object of many studies. The use of models of forecast of univariate time series stands out as the more accurate and useful to reduce the uncertainty in the economic decision making process. This study analyzed the historical series of prices of the Brazilian natural rubber (R$/kg), in the Jan/99 - Jun/2006 period, in order to characterize the rubber price behavior in the domestic market; estimated a model for the time series of monthly natural rubber prices; and foresaw the domestic prices of the natural rubber, in the Jul/2006 - Jun/2007 period, based on the estimated models. The studied models were the ones belonging to the ARIMA family. The main results were: the domestic market of the natural rubber is expanding due to the growth of the world economy; among the adjusted models, the ARIMA (1,1,1) model provided the best adjustment of the time series of prices of the natural rubber (R$/kg); the prognosis accomplished for the series supplied statistically adequate fittings.