### Abstract

Simultaneous-equation bias adjustment of the binary regression coefficients of farm-level risk factors for lice (Bovicola ovis) in Queensland sheep flocks was undertaken to control for the interdependency between lice prevalence and their control. Using probit analysis and a two-stage estimation procedure, the correlation between the error terms and the explanatory variables was removed - resulting in coefficient estimates that were asymptotically unbiased. The data for the study were derived from a cross-sectional study of 342 Queensland farms obtained by postal questionnaire in February 1993. The outcome variable of interest was the frequency of flock lice infestation which was classified into two groups: nil versus lice each of the last 3 years. Probit analysis was used to estimate the regression coefficients of the binary explanatory variables chosen for examination: ability to maintain sheep-proof boundary fences and method of post-shearing lice treatment (backliner or dip). Removal of the simultaneous-equation bias (SEB) importantly reduced the calculated probability of a farm being infested with lice. No change in associated probabilities for farms using backliner or relative to the fencing practice occurred when the SEB was removed. A table is presented that shows all possible combinations of the explanatory variables and can be used to assess the probability of lice infestation.

Original language | English (US) |
---|---|

Pages (from-to) | 49-55 |

Number of pages | 7 |

Journal | Preventive Veterinary Medicine |

Volume | 28 |

Issue number | 1 |

DOIs | |

State | Published - Jan 1 1996 |

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### Keywords

- Australia
- Lice
- Sheep
- Simultaneous-equation bias

### ASJC Scopus subject areas

- Food Animals
- Animal Science and Zoology

### Cite this

*Preventive Veterinary Medicine*,

*28*(1), 49-55. https://doi.org/10.1016/0167-5877(96)01016-1

**Simultaneous-equation bias adjustment of the binary regression coefficients of farm-level risk factors for lice (Bovicola ovis) in sheep flocks in Queensland, Australia.** / Pearse, Baden H.G.; Carpenter, Tim; Bodman, P. M.

Research output: Contribution to journal › Article

*Preventive Veterinary Medicine*, vol. 28, no. 1, pp. 49-55. https://doi.org/10.1016/0167-5877(96)01016-1

}

TY - JOUR

T1 - Simultaneous-equation bias adjustment of the binary regression coefficients of farm-level risk factors for lice (Bovicola ovis) in sheep flocks in Queensland, Australia

AU - Pearse, Baden H.G.

AU - Carpenter, Tim

AU - Bodman, P. M.

PY - 1996/1/1

Y1 - 1996/1/1

N2 - Simultaneous-equation bias adjustment of the binary regression coefficients of farm-level risk factors for lice (Bovicola ovis) in Queensland sheep flocks was undertaken to control for the interdependency between lice prevalence and their control. Using probit analysis and a two-stage estimation procedure, the correlation between the error terms and the explanatory variables was removed - resulting in coefficient estimates that were asymptotically unbiased. The data for the study were derived from a cross-sectional study of 342 Queensland farms obtained by postal questionnaire in February 1993. The outcome variable of interest was the frequency of flock lice infestation which was classified into two groups: nil versus lice each of the last 3 years. Probit analysis was used to estimate the regression coefficients of the binary explanatory variables chosen for examination: ability to maintain sheep-proof boundary fences and method of post-shearing lice treatment (backliner or dip). Removal of the simultaneous-equation bias (SEB) importantly reduced the calculated probability of a farm being infested with lice. No change in associated probabilities for farms using backliner or relative to the fencing practice occurred when the SEB was removed. A table is presented that shows all possible combinations of the explanatory variables and can be used to assess the probability of lice infestation.

AB - Simultaneous-equation bias adjustment of the binary regression coefficients of farm-level risk factors for lice (Bovicola ovis) in Queensland sheep flocks was undertaken to control for the interdependency between lice prevalence and their control. Using probit analysis and a two-stage estimation procedure, the correlation between the error terms and the explanatory variables was removed - resulting in coefficient estimates that were asymptotically unbiased. The data for the study were derived from a cross-sectional study of 342 Queensland farms obtained by postal questionnaire in February 1993. The outcome variable of interest was the frequency of flock lice infestation which was classified into two groups: nil versus lice each of the last 3 years. Probit analysis was used to estimate the regression coefficients of the binary explanatory variables chosen for examination: ability to maintain sheep-proof boundary fences and method of post-shearing lice treatment (backliner or dip). Removal of the simultaneous-equation bias (SEB) importantly reduced the calculated probability of a farm being infested with lice. No change in associated probabilities for farms using backliner or relative to the fencing practice occurred when the SEB was removed. A table is presented that shows all possible combinations of the explanatory variables and can be used to assess the probability of lice infestation.

KW - Australia

KW - Lice

KW - Sheep

KW - Simultaneous-equation bias

UR - http://www.scopus.com/inward/record.url?scp=22244454116&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=22244454116&partnerID=8YFLogxK

U2 - 10.1016/0167-5877(96)01016-1

DO - 10.1016/0167-5877(96)01016-1

M3 - Article

AN - SCOPUS:22244454116

VL - 28

SP - 49

EP - 55

JO - Preventive Veterinary Medicine

JF - Preventive Veterinary Medicine

SN - 0167-5877

IS - 1

ER -