Further comparison of faecal egg count reduction test procedures: Sensitivity and specificity

Extract

In a recent communication (McKenna2006), a comparison was made between four different methods for calculating results from faecal egg count reduction (FECR) tests (FECRTs). The first and most complex of these, referred to as FECRT₁, involved the use of the formula: FECR = 100 × (1−[T2/T1][C1/C2]), where T1 and T2 represented the mean pre- and post-treatment faecal nematode egg counts (FECs) of a treated group, and C1 and C2 represented the mean pre- and post-treatment FECs of an untreated control group, respectively. The other three formulae consisted of more simplified versions of this procedure. In one of them (FECRT₂), only post-treatment samples were considered, whereas the other two were based on comparisons between the FECs of groups of animals sampled at the time of anthelmintic treatment (pre-treatment) with those sampled several days later (post-treatment). Thus, FECRT₂ was determined according to the formula: FECR = 100 × (1−[T2/C2]), while FECRT₃ was calculated from FECR = 100 × (1−[T2/T1]). The fourth procedure (FECRT₄) was based on a further simplification of FECRT₃ where pre-treatment FECs from only one treatment group were used for comparison with all post-treatment results. This base-line pre-treatment group thus effectively functioned as an untreated control group and hence the formula for FECRT₄ was FECR = 100 × (1−[T2/C1]).