K-41 
Advantages of new method over Wilcoxon’s 
Wilcoxon 
• evaluates differences in distributions based on ranks, cannot quantify 
magnitude of shift 
• sensitive to small shifts in distribution of B-lBI scores 
New method 
• estimates proportion of area below thresholds and magnitude of 
departure from reference conditions 
• tests if this magnitude is above specific thresholds of protection 
• incorporates uncertainty in reference conditions as well as sampling 
variability in the assessment data 
• does not require purchase of special statistical analysis package 
(Wilcoxon does) 
• Both methods are suitable for data segregated into multiple habitats for 
which reference distributions are not homogeneous 
appendix k 
2006 303(d) Assessment Methods for Chesapeake Bay Benthos 
