Conclusions QUAMP study
Small negative biases seem to exist for all crops except Durum Wheat which has a small positive bias. These biases however are not statistically significant. This is one reason why Durum Wheat's yield error was much different from that of the other crops. The size of error (MAPE) is mainly at the 3-6% interval, except for Durum Wheat where it is larger than 6%. In general, Soft wheat and Barley have the smallest errors, while Durum wheat, Rape seed and Sunflower have the largest ones.
Most crops were underestimated in most countries. In two combinations of crop, country (i.e. Potato and Sugar beet in Spain ) this underestimation was found significantly large. Also Grain maize was underestimated on average in all countries, Potato was underestimated in 12 out of the 14 countries (Luxemburg excluded), and Sunflower yield was overestimated in all countries except Austria. It is also worth noting that the yield in Belgium was underestimated for all crops while in Germany it was underestimated for 7 out of 8 crops. On the contrary, yields in Italy appear to be overestimated on average in 6 out of 8 crops. Observing the size of error it can be observed that the largest error occurs in Spain , Portugal and Finland (and to a lesser extend Greece and Ireland ). On the other hand the smallest error occurs in Denmark , France and Belgium . It is worth noting that the former group mostly consists of countries in the periphery of the EU and the latter consists of countries which are geographically close.
Evolution across months
Bias appears to decrease in each consecutive month with the exception of July where it actually increases for all crops. This decrease, as expected, leads to more reliable results later in the campaign. The only statistically significant bias occurs in the October prediction of Grain maize. The size of error also decreases for all crops. The average change of MAPE per month for EU-15 appears larger for Durum wheat (-1.23%) and Potato (-0.77%) with Sunflower (-0.14%), Barley (-0.27%) and Rape seed (-0.27%) reporting the smallest changes. The large value of the reduction for Durum wheat appears more reasonable if we consider that it starts with the largest error.
Evolution across years
No significant trend appears to exist throughout the years although in the last years (2000, 2001) mostly negative biases have turned to positive ones.The size of error appears to be falling from year to year but different crops have widely different behaviours.