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Zero adjusted models with applications to analysing helminths count data.

Chipeta MG, Ngwira BM, Simoonga C, Kazembe LN - BMC Res Notes (2014)

Bottom Line: Main objective of the current paper is to apply such models to analyse risk factors associated with human helminths (S. haematobium) particularly in a case where there's a high proportion of zero counts.With regards to zero count capturing, these models performed better than other models.The choice between the hurdle and zero-inflated models should be based on the aim and endpoints of the study.

View Article: PubMed Central - PubMed

Affiliation: Malawi Liverpool - Wellcome Trust Clinical Research Programme, PO Box 30096, Blantyre, Malawi. mikechipeta@yahoo.co.uk.

ABSTRACT

Background: It is common in public health and epidemiology that the outcome of interest is counts of events occurrence. Analysing these data using classical linear models is mostly inappropriate, even after transformation of outcome variables due to overdispersion. Zero-adjusted mixture count models such as zero-inflated and hurdle count models are applied to count data when over-dispersion and excess zeros exist. Main objective of the current paper is to apply such models to analyse risk factors associated with human helminths (S. haematobium) particularly in a case where there's a high proportion of zero counts.

Methods: The data were collected during a community-based randomised control trial assessing the impact of mass drug administration (MDA) with praziquantel in Malawi, and a school-based cross sectional epidemiology survey in Zambia. Count data models including traditional (Poisson and negative binomial) models, zero modified models (zero inflated Poisson and zero inflated negative binomial) and hurdle models (Poisson logit hurdle and negative binomial logit hurdle) were fitted and compared.

Results: Using Akaike information criteria (AIC), the negative binomial logit hurdle (NBLH) and zero inflated negative binomial (ZINB) showed best performance in both datasets. With regards to zero count capturing, these models performed better than other models.

Conclusion: This paper showed that zero modified NBLH and ZINB models are more appropriate methods for the analysis of data with excess zeros. The choice between the hurdle and zero-inflated models should be based on the aim and endpoints of the study.

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Related in: MedlinePlus

Distribution of egg counts forS. haematobiumin Malawi study.
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Related In: Results  -  Collection

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Fig1: Distribution of egg counts forS. haematobiumin Malawi study.

Mentions: Figure1 shows that a large proportion of individuals i.e. 85.8% for S. haematobium were "zero egg excretors". The likelihood ratio test for over-dispersion between Poisson and Negative binomial at α = 0.05 showed a critical value test statistic = 2.7 with a χ2 test statistic = 10606.5, p-value < 0.001. Indeed, there was overwhelming evidence of overdispersion. This was confirmed by the presence of excess zeros (Figure1).Figure 1


Zero adjusted models with applications to analysing helminths count data.

Chipeta MG, Ngwira BM, Simoonga C, Kazembe LN - BMC Res Notes (2014)

Distribution of egg counts forS. haematobiumin Malawi study.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4289350&req=5

Fig1: Distribution of egg counts forS. haematobiumin Malawi study.
Mentions: Figure1 shows that a large proportion of individuals i.e. 85.8% for S. haematobium were "zero egg excretors". The likelihood ratio test for over-dispersion between Poisson and Negative binomial at α = 0.05 showed a critical value test statistic = 2.7 with a χ2 test statistic = 10606.5, p-value < 0.001. Indeed, there was overwhelming evidence of overdispersion. This was confirmed by the presence of excess zeros (Figure1).Figure 1

Bottom Line: Main objective of the current paper is to apply such models to analyse risk factors associated with human helminths (S. haematobium) particularly in a case where there's a high proportion of zero counts.With regards to zero count capturing, these models performed better than other models.The choice between the hurdle and zero-inflated models should be based on the aim and endpoints of the study.

View Article: PubMed Central - PubMed

Affiliation: Malawi Liverpool - Wellcome Trust Clinical Research Programme, PO Box 30096, Blantyre, Malawi. mikechipeta@yahoo.co.uk.

ABSTRACT

Background: It is common in public health and epidemiology that the outcome of interest is counts of events occurrence. Analysing these data using classical linear models is mostly inappropriate, even after transformation of outcome variables due to overdispersion. Zero-adjusted mixture count models such as zero-inflated and hurdle count models are applied to count data when over-dispersion and excess zeros exist. Main objective of the current paper is to apply such models to analyse risk factors associated with human helminths (S. haematobium) particularly in a case where there's a high proportion of zero counts.

Methods: The data were collected during a community-based randomised control trial assessing the impact of mass drug administration (MDA) with praziquantel in Malawi, and a school-based cross sectional epidemiology survey in Zambia. Count data models including traditional (Poisson and negative binomial) models, zero modified models (zero inflated Poisson and zero inflated negative binomial) and hurdle models (Poisson logit hurdle and negative binomial logit hurdle) were fitted and compared.

Results: Using Akaike information criteria (AIC), the negative binomial logit hurdle (NBLH) and zero inflated negative binomial (ZINB) showed best performance in both datasets. With regards to zero count capturing, these models performed better than other models.

Conclusion: This paper showed that zero modified NBLH and ZINB models are more appropriate methods for the analysis of data with excess zeros. The choice between the hurdle and zero-inflated models should be based on the aim and endpoints of the study.

Show MeSH
Related in: MedlinePlus