Improvement of MCYFS forecasts

The purpose of this section is to examine whether the performance of MCYFS in the period 1998-2002 improved compared to its performance in the period 1993-1997. Performance is assessed in terms of average error size and more specifically in terms of RMSPE.

Separately for each crop monthly RMSPE have been computed averaging the MCYFS errors, for the given month, during the two periods in question. Errors refer to EU-total forecasts. EU-total denotes EU12 until 1995 and EU15 from 1996 onwards.

Moreover, a Wilcoxon test on each month's absolute percentage errors is applied to test the null hypothesis (H 0) that absolute percentage errors have not improved (i.e. have not decreased) during the period 1998-2002 as opposed to the period 1993-1997. Therefore small p-values (less than 0.05 in this document) reject the null hypothesis and show improvement (reduction) of errors and hence better performance of MCYFS.

Soft wheat

The monthly RMSPEs of MCYFS in the forecasting of Soft wheat and the p-values of the respective Wilcoxon tests are reported in the following table: MONTH RMSPE 93-02 RMSPE 93-97 RMSPE 98-02 P-VALUE March 4.16 4.16 April 4.37 5.05 3.73 0.2778 May 4.37 4.82 3.87 0.7262 June 4.19 4.98 3.21 0.5317 July 5.02 5.47 1.37 0.5000 August 3.45 4.52 1.85 0.1111 September 3.39 3.60 2.05 0.3333 October 3.09 3.80 2.18 0.2429 November 0.13 0.13 Overall 4.00 4.66 3.15 The RMSPE in 1998-2002 is smaller than the respective RMSPE of 1993-1997 in all months; the differences however are not statistically significant. The lack of significance is partly due to the sparseness of the data from which these figures are derived. However, there are strong indications that MCYFS has improved in the forecasting of Soft wheat yield after 1998. The contents of the table are presented graphically in the following diagram:

Durum wheat

The monthly RMSPEs of MCYFS in the forecasting of Durum wheat and the p-values of the respective Wilcoxon tests are the following: MONTH RMSPE 93-02 RMSPE 93-97 RMSPE 98-02 P-VALUE March 16.52 16.52 April 26.32 37.66 10.61 0.0556 May 26.27 36.57 6.58 0.0278 June 23.95 35.41 5.42 0.0317 July 33.26 36.42 2.09 0.1667 August 25.91 36.41 4.03 0.0278 September 33.52 36.56 7.60 0.5000 October 25.14 35.28 4.40 0.1000 November 1.99 1.99 Overall 26.59 36.36 8.50 Note: Bold values indicate significant cases at the 0.05 level. The RMSPE in 1998-2002 for Durum wheat is smaller than the respective RMSPE of 1993-1997 in all months. The improvement in May, June and August is considered statistically significant. Moreover, the p-values of April, July and October are small. Therefore, there are very strong indications that MCYFS has improved in the forecasting of Durum wheat yield after 1998. The contents of the table are displayed in the following graph:

Barley

The monthly RMSPEs of MCYFS in the forecasting of Barley and the p-values of the Wilcoxon tests are reported in the following table: MONTH RMSPE 93-02 RMSPE 93-97 RMSPE 98-02 P-VALUE March 3.63 3.63 April 3.89 4.46 3.36 0.8571 May 3.53 4.49 2.18 0.3730 June 3.44 4.44 1.98 0.2103 July 3.93 4.29 0.74 0.1667 August 2.74 3.39 1.87 0.4206 September 2.95 3.21 0.83 0.3333 October 1.65 1.68 1.62 0.6571 November 0.74 0.74 Overall 3.24 3.86 2.42 The RMSPE in 1998-2002 is smaller than the respective RMSPE of 1993-1997 in all months; the improvements however are not considered statistically significant. Data sparseness may be partly responsible for this outcome. There are however indications that MCYFS has improved in the forecasting of Barley yield after 1998. The contents of the table are presented in the following graph:

Grain maize

The monthly RMSPEs of MCYFS in the forecasting of Grain maize and the p-values of the Wilcoxon tests are the following: MONTH RMSPE 93-02 RMSPE 93-97 RMSPE 98-02 P-VALUE March April 6.26 7.75 2.80 0.2000 May 4.73 6.76 1.95 0.0556 June 4.18 5.73 1.46 0.0159 July 5.07 5.55 0.58 0.1667 August 4.04 5.33 2.03 0.0278 September 4.08 4.43 2.16 0.4000 October 3.43 4.62 1.47 0.0143 November 2.77 2.77 Overall 4.46 5.74 1.91 Note: Bold values indicate significant cases at the 0.05 level. The RMSPE in 1998-2002 is smaller than the respective RMSPE of 1993-1997 in all months. The improvement in June, August and October is considered statistically significant. Moreover, the p-values of April, May and July are small. Therefore, there are very strong indications that MCYFS has improved in the forecasting of Grain maize yield after 1998.The contents of the table are presented in the following diagram: RMSPEs after 1998 are definitely smaller than those before 1998. The improvement is slightly smaller in the second half of the year than in the first.

Rape seed

The monthly RMSPEs of MCYFS in the forecasting of Rape seed and the p-values of the Wilcoxon tests are the following: MONTH RMSPE 93-02 RMSPE 93-97 RMSPE 98-02 P-VALUE March 6.77 6.77 April 7.33 6.46 7.95 May 6.86 6.63 7.04 June 5.09 4.83 5.29 July 4.96 4.83 5.46 August 4.99 5.54 4.50 0.6349 September 5.09 5.54 2.64 0.6000 October 4.92 5.54 4.22 0.6571 November 5.46 5.46 Overall 5.86 5.66 6.03 The RMSPE in 1998-2002 is greater than the respective RMSPE of 1993-1997 from April until July, and smaller thereafter. No statistically significant improvement in 1998-2002 is detected. The figure shows that RMSPEs after 1998 are greater than those before 1998 for all months up to July. The only month where RMSPEs denote improvement after 1998 is September.

Potato

The monthly RMSPEs of MCYFS in the forecasting of Potato and the p-values of the Wilcoxon tests are the following: MONTH RMSPE 93-02 RMSPE 93-97 RMSPE 98-02 P-VALUE March April 6.89 6.89 May 3.75 4.80 3.09 0.1333 June 6.12 8.26 2.57 0.1714 July 6.99 7.80 1.10 0.2000 August 5.36 7.56 2.44 0.0317 September 4.90 5.47 0.47 0.2000 October 3.77 5.07 1.64 0.0143 November 0.81 0.81 Overall 5.26 6.80 2.32 Note: Bold values indicate significant cases at the 0.05 level. The RMSPE in 1998-2002 is smaller than the respective RMSPE of 1993-1997 in all months. The improvement in August and October is considered statistically significant. Moreover, the p-values of May, June, July and September are small. Therefore, there are very strong indications that MCYFS has improved in the forecasting of Potato yield after 1998.

Sugar beet

The monthly RMSPEs of MCYFS in the forecasting of Sugar beet and the p-values of the Wilcoxon tests are the following: MONTH RMSPE 93-02 RMSPE 93-97 RMSPE 98-02 P-VALUE March April 4.56 4.56 May 4.95 4.65 5.17 June 5.83 6.17 5.38 0.4524 July 4.68 4.22 6.18 August 7.87 3.34 10.62 September 1.99 2.13 1.08 0.1667 October 3.35 1.33 4.28 November 2.96 2.96 Overall 5.38 4.09 6.74 The RMSPE in 1998-2002 is greater than the respective RMSPE of 1993-1997 in all months except June and September. No statistically significant improvement in 1998-2002 is detected. The graphical representation of the table is shown below: RMSPEs after 1998 are greater than those before 1998 for all months, except June and September. Especially in August, after 1998 RMSPEs are much worse than before 1998.

Sunflower

The monthly RMSPEs of MCYFS in the forecasting of Sunflower and the p-values of the Wilcoxon tests are the following: MONTH RMSPE 93-02 RMSPE 93-97 RMSPE 98-02 P-VALUE March April 14.06 14.06 May 11.29 17.35 3.44 0.1000 June 7.50 6.59 8.30 July 7.15 7.15 August 4.92 3.46 6.04 September 7.13 7.70 4.12 0.4000 October 6.80 7.70 5.77 0.2429 November Overall 7.91 8.89 6.16 The RMSPE in 1998-2002 is greater than the respective RMSPE of 1993-1997 from June until August. No statistically significant improvement in 1998-2002 is detected. The p-value of May however is quite small.