K-37 
Summary (cont.) 
• Reference distributions are sometimes based on a small number of 
samples; therefore the 5 lh percentile score is not well defined 
• The S'* percentile score and its variance was estimated by bootstrap 
simulations 
• For each iteration of the bootstrap simulation, a subset of the good 
reference data for each habitat was selected at random, and the 5 11 
percentile score determined 
• Over all the iterations, the 5* 1 percentile score varied, and at each iteration 
the threshold was established according to the rule described earlier 
• See next slide for the two habitat examples 
appendix k 
2006 303(d) Assessment Methods for Chesapeake Bay Benthos 
