Table 1.

Classes of minimum detectable differences (MDD) as proposed in the EFSA Aquatic Guidance Document

MDD class	%MDD	Comment
0	>100 %	No effects can be determined statistically
I	90–100 %	Only large effects can be determined statistically
II	70–90 %	Large to medium effects can be determined statistically
III	50–70 %	Medium effects can be determined statistically
IV	<50 %	Small effects can be determined statistically

Source: EFSA 2013)

Note that these classes apply to treatment-related reductions in abundance/biomass of taxa in particular, since the MDD may be larger than 100 % while treatment-related increases in abundance/biomass may still be demonstrated. We have assumed that the MDD in the EFSA Aquatic Guidance document would equal the MDD_abu as defined in this manuscript