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Titolo:
MODELING THE EFFECT OF A DISEASE ON CULLING - AN ILLUSTRATION OF THE USE OF TIME-DEPENDENT COVARIATES FOR SURVIVAL ANALYSIS
Autore:
GROHN YT; DUCROCQ V; HERTL JA;
Indirizzi:
CORNELL UNIV,COLL VET MED,DEPT CLIN SCI,EPIDEMIOL SECT ITHACA NY 14853 CORNELL UNIV,COLL AGR & LIFE SCI,DEPT ANIM SCI ITHACA NY 14853
Titolo Testata:
Journal of dairy science
fascicolo: 8, volume: 80, anno: 1997,
pagine: 1755 - 1766
SICI:
0022-0302(1997)80:8<1755:MTEOAD>2.0.ZU;2-L
Fonte:
ISI
Lingua:
ENG
Soggetto:
LIFE; COWS;
Keywords:
SURVIVAL ANALYSIS; TIME-DEPENDENT COVARIATE; COX MODEL; WEIBULL MODEL;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Science Citation Index Expanded
Citazioni:
11
Recensione:
Indirizzi per estratti:
Citazione:
Y.T. Grohn et al., "MODELING THE EFFECT OF A DISEASE ON CULLING - AN ILLUSTRATION OF THE USE OF TIME-DEPENDENT COVARIATES FOR SURVIVAL ANALYSIS", Journal of dairy science, 80(8), 1997, pp. 1755-1766

Abstract

This study demonstrated five different approaches, with and without time-dependent covariates, to determine the effect of disease on culling. It was also of interest to determine whether the time of the disease had an effect on subsequent culling (i.e., whether disease should betreated as a time-dependent covariate). To this purpose, five separate models were studied: Models 1 through 4 were Cox proportional hazards models, and Model 5 was a Weibull model. Model 1 treated disease as a binary, time-independent covariate. Model 2 treated disease as a time-dependent covariate, and one change of status was assumed to occur at the time of disease. Model 3 also assumed that one change in status occurred at the time of disease, but the effect of that change was assumed to be different depending on when the disease occurred. Models 4 (Cox) and 5 (Weibull) assumed an interaction between the occurrence ofdisease (time of disease) and the occurrence of culling (time of culling). As an illustration, the effect of mastitis on culling was studied for 2998 Holstein dairy cows in 10 herds. Parity and previous 305-d milk yield were also included as covariates; the data were stratified by herd. For all models, mastitis was a significant factor for culling. The significance tests for the estimates from Models 4 and 5 demonstrated that the hazard of culling differed for different stages of lactation, depending on when mastitis had occurred and when its effect on culling occurred; that is, time dependence exists between time of mastitis and time of culling.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 04/12/20 alle ore 22:00:30