Efficacy of Emamectin Benzoate Table 3. Percentages of emamectin benzoate episodes classified according to each of the variables included in the GLM. Table 4. Results of the GLM analysis of sea lice abundance following emamectin benzoate treatment. Variable #Days after treatment 7–13 % of treatments (N = 108) Class 14–20 21–27 28–34 35–41 42–48 49–55 56–62 63–69 70–76 77–83 North South 2002 2003 2004 2005 2006 1st 2nd No Yes No Yes Western Isles Spring (Feb–Apr) Summer (May–Jul) Autumn (Aug–Oct) Winter (Nov–Jan) 59% 68% 66% 56% 67% 59% 61% 58% 52% 47% 42% 36% 33% 31% 9% 19% 29% 28% 15% 45% 55% 28% 30% 30% 13% 18% 82% 53% 47% Region Year Production year Season Effective Loch-wide #- ‘‘% of treatments’’ for the variable ‘‘Days after treatment’’ refers to the percentage of treated farms that were monitored for sea lice in each 7-day time period following treatment. doi:10.1371/journal.pone.0001549.t003 interval associated with the spring value indicates that this result should be treated with caution. A significant interaction also existed between the season in which the treatment was applied and loch-wide interventions (Figure 4C). Lice abundance following winter loch-wide treat- ments (4.87, CI [3.61–6.46]) was found to be significantly higher (p,0.05) than after any emamectin benzoate intervention applied in other seasons, except for loch-wide treatments applied in spring (3.75, CI [2.79–4.95]). Discussion By adopting an epi-informatics approach and examining a large historical data set, the efficacy of emamectin benzoate treatments administered over a five year period, at different stages of production and across three Scottish regions was shown to vary significantly. While commercial farm records provide a rich source of information, working with production data can present some Table indicates those variables found to be statistically significant (p,0.05) within the model and provides estimates of post-treatment mobile L. salmonis abundances and their 95% confidence intervals. #- Forced co-variate with coefficient of 0.16 (95% CI [0.11–0.22]) doi:10.1371/journal.pone.0001549.t004 challenges. Only when a large data set is available is it possible to extract data of sufficient quality and quantity to perform meaningful analysis. The routine lice monitoring programme that was in place allowed 58% of the site-wide emamectin benzoate treatments administered between 2002 and 2006 to be included in the efficacy analysis. Two previous studies that used production data to assess the efficacy of emamectin benzoate in British Columbia [23] and on the Maine coast [28] encountered similar challenges, with fewer than 20 treatment episodes remaining PLoS ONE | www.plosone.org 7 February 2008 | Volume 3 | Issue 2 | e1549 Variable # Pre-treatment mobile abundance Days after treatment p-value Class 0.00 0.00 Region Year Production year Season Effective Loch-wide Region6Year Season6Effective Season6Loch-wide 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - 7–13 14–20 21–27 28–34 35–41 42–48 49–55 56–62 63–69 70–76 77–83 North South 2002 2003 2004 2005 2006 1st 2nd Western Isles Spring (Feb–Apr) Summer (May–Jul) 2.13 Autumn (Aug–Oct) 2.10 Winter (Nov–Jan) No Yes No Yes See Figure 4 - 3.83 2.84 2.29 2.19 2.39 2.24 2.24 2.52 2.80 2.97 2.94 2.08 3.10 2.80 1.96 2.48 2.97 2.61 3.27 2.30 3.00 3.24 3.24 7.01 0.65 2.16 3.17 Post-treatment mobile abundance Least squares mean 95% CI - [3.23–4.51] [2.40–3.34] [1.89–2.74] [1.80–2.65] [1.98–2.86] [1.83–2.71] [1.84–2.71] [2.07–3.04] [2.29–3.38] [2.42–3.61] [2.37–3.61] [1.79–2.39] [2.68–3.58] [2.40–3.24] [1.53–2.47] [2.05–2.97] [2.61–3.37] [2.28–2.98] [2.74–3.87] [2.00–2.63] [2.60–3.44] [2.52–4.10] [1.67–2.67] [1.75–2.49] [2.61–3.98] [5.95–8.22] [0.55–0.75] [1.89–2.45] [2.79–3.59]