### Abstract

Objective-To develop a method of probability diagnostic, assignment (PDA) that uses continuous serologic measures and infection prevalence to estimate the probability of an animal being infected, using Neospora caninum as an example. Animals-196 N caninum-infected beef and dairy cattle and 553 cattle not infected with N caninum; 50 dairy cows that aborted and 50 herdmates that did not abort. Procedure-Probability density functions corresponding to distributions of N caninum kinetic ELISA results from infected and uninfected cattle were estimated by maximum likelihood methods. Maximum likelihood methods also were used to estimate N caninum infection prevalence in a herd that had an excessive number of abortions. Density functions and the prevalence estimate were incorporated into Bayes formula to calculate the conditional probability that a cow with a particular ELISA value was infected with N caninum. Results-Probability functions identified for infected and uninfected cattle were Weibull and inverse gamma functions, respectively. Herd prevalence was estimated, and probabilities of N caninum infection were determined for cows with various ELISA values. Conclusions and Clinical Relevance-Use of PDA offers an advantage to clinicians and diagnosticians over traditional seronegative or seropositive classifications used as a proxy for infection status by providing an assessment of the actual probability of infection. The PDA permits use of all diagnostic information inherent in an assay, thereby eliminating a need for estimates of sensitivity and specificity. The PDA also would have general utility in interpreting results of any diagnostic assay measured on a continuous or discrete scale.

Original language | English (US) |
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Pages (from-to) | 318-325 |

Number of pages | 8 |

Journal | American Journal of Veterinary Research |

Volume | 63 |

Issue number | 3 |

DOIs | |

State | Published - Mar 1 2002 |

### ASJC Scopus subject areas

- veterinary(all)

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## Cite this

*American Journal of Veterinary Research*,

*63*(3), 318-325. https://doi.org/10.2460/ajvr.2002.63.318