Type I errors linked to faulty statistical analyses of endangered subspecies classifications

Legal issues related to subspecies identification frequently occur through the implementation of the 1973 Endangered Species Act (ESA). A listing under the ESA requires management actions to ensure the continued existence of the taxa. However, these actions often have important social, economic, and political implications. We examined the statistical methods of morphological analysis used in subspecies identification. Methods are illustrated using the California gnatcatcher (Polioptila californica), which was incorrectly listed under the ESA due to misinterpretation of morphological data. We found that inferences based on tests of sample means (i.e., t-test, Hotelling’s T ²-statistics), cluster analysis, and discriminant analysis were subject to high rates of false positives (identification of subspecies when none exist; Type I error). These simple tests ignore the common occurrence of spatial clines in animal tracts. Alternatively, spline-regression and step-regression procedures were found to be quite robust yet had high resolution in finding subspecies break locations.     

Efficacy of vaccination and antimicrobial treatment to eliminate chronic intramammary Staphylococcus aureus infections in dairy cattle

OBJECTIVE: To determine whether a combination of vaccination and extended intramammary antimicrobial treatment would eliminate chronic intramammary Staphylococcus aureus infections in lactating dairy cows. DESIGN: Randomized controlled clinical trial. ANIMALS: 50 dairy cows with chronic mastitis caused by S aureus. PROCEDURE: Cows were identified and paired within herd on the basis of days in milk, lactation number, milk production, and numbers of quarters infected. Treated cows (n=20) received 3 doses of a polyvalent S aureus bacterin on days 1, 15, and 21 of the study along with intramammary administration of pirlimycin in all 4 quarters once daily for 5 treatments (days 16 to 20). Control cows (n=23) received no treatment. Follow-up samples for bacteriologic culture were collected for at least 3 months after treatment to determine treatment success rates. RESULTS: Significantly more S aureus infections were eliminated from treated cows (8/20 [40%]), compared with control cows (2/23 [9%]). The proportion of infected quarters that yielded negative results throughout the follow-up period was also significantly higher in treated cows (13/28 [46%]) than in control cows (2/41 [5%]). CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that a combination of vaccination and antimicrobial treatment can be successful in eliminating some cases of chronic intramammary S aureus infections in dairy cattle. However, it is important to consider extended treatment protocols carefully because many cows are likely to remain infected with S aureus despite treatment and vaccination.