Estimation in zero-inflated binomial regression with missing covariates

Modelling of vertical integration in commercial poultry production of Ghana: A count data model analysis

Poultry production has significant potential to reduce protein deficiency, food insecurity and poverty in Ghana. However, limited vertical integration and high cost of production in the sector have stifled growth and exposed poultry farms in the country to many risks, leading to poor business performance. This study uses cross-sectional data from 102 commercial poultry farms to assess the determinants of vertical integration in the Ghanaian poultry industry by employing zero-inflated Poisson (ZIP) and Zero-inflated Negative Binomial (ZINB) models. The results show that one in every four poultry farms in the country are vertically integrated, either partially or fully. The ZINB model, which best fits the data, reveals that the degree of vertical integration in the poultry business is significantly influenced by a set of personal (education, occupation, and farming experience) and farm level (land tenure, flock size, production cost, and farm revenue) characteristics as well as institutional factors (credit access, extension access and membership of association). The paper discusses the implications of these findings and provides appropriate recommendations for strengthening the poultry industry in Ghana.

Modelling count data with an excess of zero values applied to childhood bone tumour incidence in Iraq

Bone tumours are rarely found in children and adolescents (0- 19 years old), but there are reports from some provinces in Iraq indicating possible increases in the incidence of childhood bone cancer. Since counts are very low and often zero, or near zero, we fitted zero-inflated Poisson, zero-inflated negative binomial, Poisson hurdle, and negative binomial hurdle regression models to investigate these changes. We used data covering the 2000-2015 period taking age, gender and province into account with the aim of identifying potential health disparities. The results indicate that the zero-inflated Poisson is the most appropriate approach. We also found that, the incidence rate ratio of bone tumours for age groups of 5-9, 10-14 and 15-19 years were 134%, 490% and 723% higher, respectively, compared to the 0-4 year olds. The incidence rate was higher by 49% higher in males compared to females. Compared to 2000-2004, the rate was higher during 2005-2009 and 2010-2015 by 23% and 50%, respectively. In addition, the provinces Al-Muthana and Al-Diwaniyah in the South were found to have a higher incidence rate than other provinces. Join point analysis showed that the age-adjusted incidence rate had a significant, increasing trend, with an average percentage change of 3.1% during 2000-2015. The study suggests that further research into childhood tumours, bone tumours in particular, is needed. Reference to the effect of environmental factors in this group of medical disorders would be of special interest.