The descriptive statistics (Table 4.1) demonstrate the low levels of variance in ecological diversity within the relevant areas, and is supportive of the Zonal Characterisation results (MESL, 2011). Table 4.1 demonstrates the relatively higher variance in Shannon diversity index when compared with the Simpson index. This may result in a higher ESN for Shannon to reach the critical Power threshold (0.8) when compared with Simpson. The table also shows the number of stations surveyed in 2010/2011 present within East Anglia THREE and FOUR, and the sample number used for cable corridor assessments.
Table 4.1. Descriptive statistics for Power analysis and es conversion Study
Metric Area EA
Shannon Shannon
Benthic
Simpson Simpson
Shannon Shannon
Epibenthic
Simpson Simpson
4.2 Effect Size
Table 4.2 shows the percentage changes (as Estimated Detectable Percentage Change, EDPC) in Shannon Diversity (H’) and Simpson’s Index (S) values that represent a range of effect sizes (es). The results show that this relationship is variable between Areas and between diversity index measured. The es values commonly adopted in ecological investigations (i.e. 0.2, 0.5 and 0.8, Cohen 1988) all represent changes in diversity index values of less than 20% (Table 4.2). The EDPC values at these effect sizes are all lower than would be considered required as part of an Impact Assessment, on the basis that a 50% change in a diversity index would be accepted by the statutory authority.
