### 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 |

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### ASJC Scopus subject areas

- veterinary(all)

### Cite this

*American Journal of Veterinary Research*,

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

**A method of probability diagnostic assignment that applies Bayes theorem for use in serologic diagnostics, using an example of Neospora caninum infection in cattle.** / Thurmond, Mark; Johnson, Wesley O.; Muñoz-Zanzi, Claudia A.; Su, Chun Lung; Hietala, Sharon K.

Research output: Contribution to journal › Article

*American Journal of Veterinary Research*, vol. 63, no. 3, pp. 318-325. https://doi.org/10.2460/ajvr.2002.63.318

}

TY - JOUR

T1 - A method of probability diagnostic assignment that applies Bayes theorem for use in serologic diagnostics, using an example of Neospora caninum infection in cattle

AU - Thurmond, Mark

AU - Johnson, Wesley O.

AU - Muñoz-Zanzi, Claudia A.

AU - Su, Chun Lung

AU - Hietala, Sharon K.

PY - 2002/3/1

Y1 - 2002/3/1

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=0036521195&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0036521195&partnerID=8YFLogxK

U2 - 10.2460/ajvr.2002.63.318

DO - 10.2460/ajvr.2002.63.318

M3 - Article

C2 - 11911564

AN - SCOPUS:0036521195

VL - 63

SP - 318

EP - 325

JO - American Journal of Veterinary Research

JF - American Journal of Veterinary Research

SN - 0002-9645

IS - 3

ER -