Table 3 summarizes also the results of average year-specific and window-specific scale efficiency. As can be seen, year-specific scale scores are relatively high and lie within the ranges [89.3–94.2], [85.9–93.6], [92.1–94.6] and [86.4–92.0] for groups A, B, C and D respectively. The diagrams in the second column of Fig. 1 depict graphically the average scale efficiency trend form year-to-year. It is evident that there is a downward dominating tendency for all groups in window 2009–10 (all groups deteriorate slightly, with the exception of group B that shows an inappreciable increment). In the following window, 2010–11, all groups appear to have a sharp upward trend which is followed by a more or less downward trend in window 2011–2012. More precisely one can see that groups B and D in window 2011–12 show a relatively sharp deterioration whilst groups A and C seem to remain almost constant.