Analysis of partial and complete protection in malaria cohort studies.

Cairns, ME; Asante, KP; Owusu-Agyei, S; Chandramohan, D; Greenwood, BM; Milligan, PJ; (2013) Analysis of partial and complete protection in malaria cohort studies. Malar J, 12 (1). p. 355. ISSN 1475-2875 DOI:

Text - Published Version

Download (969kB) | Preview


BACKGROUND Malaria transmission is highly heterogeneous and analysis of incidence data must account for this for correct statistical inference. Less widely appreciated is the occurrence of a large number of zero counts (children without a malaria episode) in malaria cohort studies. Zero-inflated regression methods provide one means of addressing this issue, and also allow risk factors providing complete and partial protection to be disentangled. METHODS Poisson, negative binomial (NB), zero-inflated Poisson (ZIP) and zero-inflated negative binomial (ZINB) regression models were fitted to data from two cohort studies of malaria in children in Ghana. Multivariate models were used to understand risk factors for elevated incidence of malaria and for remaining malaria-free, and to estimate the fraction of the population not at risk of malaria. RESULTS ZINB models, which account for both heterogeneity in individual risk and an unexposed sub-group within the population, provided the best fit to data in both cohorts. These approaches gave additional insight into the mechanism of factors influencing the incidence of malaria compared to simpler approaches, such as NB regression. For example, compared to urban areas, rural residence was found to both increase the incidence rate of malaria among exposed children, and increase the probability of being exposed. In Navrongo, 34% of urban residents were estimated to be at no risk, compared to 3% of rural residents. In Kintampo, 47% of urban residents and 13% of rural residents were estimated to be at no risk. CONCLUSION These results illustrate the utility of zero-inflated regression methods for analysis of malaria cohort data that include a large number of zero counts. Specifically, these results suggest that interventions that reach mainly urban residents will have limited overall impact, since some urban residents are essentially at no risk, even in areas of high endemicity, such as in Ghana.

Item Type: Article
Faculty and Department: Faculty of Infectious and Tropical Diseases > Dept of Disease Control
Faculty of Epidemiology and Population Health > Dept of Infectious Disease Epidemiology
Research Centre: Malaria Centre
Tropical Epidemiology Group
PubMed ID: 24093726
Web of Science ID: 329097500001


Download activity - last 12 months
Downloads since deposit
Accesses by country - last 12 months
Accesses by referrer - last 12 months
Impact and interest
Additional statistics for this record are available via IRStats2

Actions (login required)

Edit Item Edit Item