Figure 5. Bootstrap relative percent difference between TBP and Ct using PCDD/F congener- and homologue-specific BSAFs and between TBP and Ct calculated using a single overall BSAF

ERDC TN-DOER-R5

September 2004

Figure 5.

Bootstrap relative percent difference between TBP and Ct using PCDD/F congener- and

homologue-specific BSAFs and between TBP and Ct calculated using a single overall BSAF

(formula in Table 4)

The relative disparity between bootstrap TBP and mean Ct, averaged over all congeners and

homologue groups, was 23 percent when congener/homologue mean BSAFs were used, and

+158 percent when the overall mean BSAF was used. Excluding homologue groups, the average

relative disparity between bootstrap TBP and mean Ct was +30 percent when congener-specific

BSAFs were used, and +176 percent when the overall mean BSAF was used.

Bootstrap Test of Significance. TBP was compared statistically with mean Ct using

bootstrap tests of significance. When TBP was calculated using congener/homologue mean

BSAFs, TBP was found to significantly underestimate mean Ct for 1,2,3,4,6,7,8-HpCDF, OCDF,

and all homologue groups except total HxCDF (bootstrap P < 0.05, Table 7). These results

correspond exactly to the comparison of mean Ct with bootstrap confidence intervals in Table 6.

However, when the overall mean BSAF was used to determine TBP, no significant differences

between mean Ct and TBP were observed in the bootstrap tests of significance.