Multilevel modelling of pre-weaning kid mortality during the cold, dry season 1991-1992 in the outskirts of N'Djaména, Chad
Résumé
The pre-weaning kid mortality during the dry, cold season in the outskirts of N'Djamena (Chad) was studied by means of data collected during an observational cohort survey of goat pneumopathies. The data set concerned 1006 kids belonging to 51 herds. Forty-eight kids died during the period of the survey (4 months). A two-level logistic model was elaborated on the basis of mixed effects models. Both individual and herd covariates were included in the model. Random effects were investigated for levels 1 and 2. Three risk factors were identified: exposure to peste des petits ruminants virus, low weight and insufficient floor space in the night housing. Half of the individual cases of mortality were poorly fitted by the model. The level-1 random parameter was significantly higher than 1, giving evidence of an extra-binomial variation. The level-2 random parameter showed that for most herds, the predicted number of dead kids was close to the observed number. Preventive measures, such as peste des petits ruminants vaccination, are proposed. The main advantages of the multilevel models are outlined