Problem eliminacji trendów podczas oceny ryzyka produkcyjnego podstawowych roślin uprawnych

Historical data of the crops yield confirms the existence of a systematic change of the average crops yield at the country level. During assessment of the production risk the overall variability of yield production is usually reduced by the variability attributed to a trend. The aim of the study was to assess the validity of such procedure. To do this, yield trends of basic crops in Poland were estimated. Afterward, the quality of the yield prediction based on the trends and the quality of the prediction based on the arithmetic mean were compared. As a measure of the prediction quality the square root of the mean squared prediction error was adopted. The study has shown that the use of the trend function leads, on average, to the lowering prediction quality by about 27%.