Anthelmintic resistance is an increasing challenge in the control of parasites in livestock. The fecal egg count reduction test (FECRT) is the practical gold standard method for evaluating resistance, but the interpretation is complicated due to high levels of variability. Several factors contribute to cause this high variability and these must be taken into account to accurately identify a reduction in anthelmintic efficacy. To address this problem, we developed a hierarchical statistical model for analysis of FECRT data from multiple farms. The model includes animal effect and farm clusters as random effects. Resistance classifications are based on model adjusted lower confidence limit (LCL) values of predicted mean efficacies on each farm. The model was used to evaluate the efficacy of pyrantel embonate paste from 64 Danish horse farms. On these farms 614 out of 1644 horses had egg counts = 200 eggs per gram (EPG) and were treated. Post treatment samples and information on age, gender and farm zip code were collected for each horse. In addition, individual coprocultureswere performed on all pretreatment fecal samples to determine the presence of Strongylus vulgaris , with 31farms (48.4 %) testing positive. The efficacy of pyrantel was unaffected by the presence of S. vulgaris on the farm. The cutoff LCL values used for classifying farms as pyrantel resistant were: >92%: no resistance, 88-92%: suspect resistance, and