Flexible modelling of risk factors on the incidence of pneumonia in young children in South Africa using piece-wise exponential additive mixed modelling

dc.contributor.authorRamjith, Jordache
dc.contributor.authorRoes, Kit C
dc.contributor.authorZar, Heather J
dc.contributor.authorJonker, Marianne A
dc.date.accessioned2021-10-11T09:23:35Z
dc.date.available2021-10-11T09:23:35Z
dc.date.issued2021-01-11
dc.date.updated2021-01-17T04:08:35Z
dc.description.abstractIntroduction Recurrent episodes of pneumonia are frequently modeled using extensions of the Cox proportional hazards model with the underlying assumption of time-constant relative risks measured by the hazard ratio. We aim to relax this assumption in a study on the effect of factors on the evolution of pneumonia incidence over time based on data from a South African birth cohort study, the Drakenstein child health study. Methods We describe and apply two models: a time-constant and a time-varying relative effects model in a piece-wise exponential additive mixed model’s framework for recurrent events. A more complex model that fits in the same framework is applied to study the continuously measured seasonal effects. Results We find that several risk factors (male sex, preterm birth, low birthweight, lower socioeconomic status, lower maternal education and maternal cigarette smoking) have strong relative effects that are persistent across time. When time-varying effects are allowed in the model, HIV exposure status (HIV exposed & uninfected versus HIV unexposed) shows a strong relative effect for younger children, but this effect weakens as children grow older, with a null effect reached from about 15 months. Weight-for-length at birth shows a time increasing relative effect. We also find that children born in the summer have a much higher risk of pneumonia in the 3-to-8-month age period compared with children born in winter. Conclusion This work highlights the usefulness of flexible modelling tools in recurrent events models. It avoids stringent assumptions and allows estimation and visualization of absolute and relative risks over time of key factors associated with incidence of pneumonia in young children, providing new perspectives on the role of risk factors such HIV exposure.en_US
dc.identifier.apacitationRamjith, J., Roes, K. C., Zar, H. J., & Jonker, M. A. (2021). Flexible modelling of risk factors on the incidence of pneumonia in young children in South Africa using piece-wise exponential additive mixed modelling. <i>BMC Medical Research Methodology</i>, 21(Article number: 17), http://hdl.handle.net/11427/35149en_ZA
dc.identifier.chicagocitationRamjith, Jordache, Kit C Roes, Heather J Zar, and Marianne A Jonker "Flexible modelling of risk factors on the incidence of pneumonia in young children in South Africa using piece-wise exponential additive mixed modelling." <i>BMC Medical Research Methodology</i> 21, Article number: 17. (2021) http://hdl.handle.net/11427/35149en_ZA
dc.identifier.citationRamjith, J., Roes, K.C., Zar, H.J. & Jonker, M.A. 2021. Flexible modelling of risk factors on the incidence of pneumonia in young children in South Africa using piece-wise exponential additive mixed modelling. <i>BMC Medical Research Methodology.</i> 21(Article number: 17) http://hdl.handle.net/11427/35149en_ZA
dc.identifier.ris TY - Journal Article AU - Ramjith, Jordache AU - Roes, Kit C AU - Zar, Heather J AU - Jonker, Marianne A AB - Introduction Recurrent episodes of pneumonia are frequently modeled using extensions of the Cox proportional hazards model with the underlying assumption of time-constant relative risks measured by the hazard ratio. We aim to relax this assumption in a study on the effect of factors on the evolution of pneumonia incidence over time based on data from a South African birth cohort study, the Drakenstein child health study. Methods We describe and apply two models: a time-constant and a time-varying relative effects model in a piece-wise exponential additive mixed model’s framework for recurrent events. A more complex model that fits in the same framework is applied to study the continuously measured seasonal effects. Results We find that several risk factors (male sex, preterm birth, low birthweight, lower socioeconomic status, lower maternal education and maternal cigarette smoking) have strong relative effects that are persistent across time. When time-varying effects are allowed in the model, HIV exposure status (HIV exposed & uninfected versus HIV unexposed) shows a strong relative effect for younger children, but this effect weakens as children grow older, with a null effect reached from about 15 months. Weight-for-length at birth shows a time increasing relative effect. We also find that children born in the summer have a much higher risk of pneumonia in the 3-to-8-month age period compared with children born in winter. Conclusion This work highlights the usefulness of flexible modelling tools in recurrent events models. It avoids stringent assumptions and allows estimation and visualization of absolute and relative risks over time of key factors associated with incidence of pneumonia in young children, providing new perspectives on the role of risk factors such HIV exposure. DA - 2021-01-11 DB - OpenUCT DP - University of Cape Town IS - Article number: 17 J1 - BMC Medical Research Methodology KW - Cox model KW - Proportional hazards KW - Time-varying effects KW - Recurrent events KW - Piece-wise exponential model KW - Additive model KW - Survival analysis LK - https://open.uct.ac.za PY - 2021 T1 - Flexible modelling of risk factors on the incidence of pneumonia in young children in South Africa using piece-wise exponential additive mixed modelling TI - Flexible modelling of risk factors on the incidence of pneumonia in young children in South Africa using piece-wise exponential additive mixed modelling UR - http://hdl.handle.net/11427/35149 ER - en_ZA
dc.identifier.urihttps://doi.org/10.1186/s12874-020-01194-6
dc.identifier.urihttp://hdl.handle.net/11427/35149
dc.identifier.vancouvercitationRamjith J, Roes KC, Zar HJ, Jonker MA. Flexible modelling of risk factors on the incidence of pneumonia in young children in South Africa using piece-wise exponential additive mixed modelling. BMC Medical Research Methodology. 2021;21(Article number: 17) http://hdl.handle.net/11427/35149.en_ZA
dc.language.isoenen_US
dc.language.rfc3066en
dc.publisher.departmentDepartment of Paediatrics and Child Healthen_US
dc.publisher.facultyFaculty of Health Sciencesen_US
dc.rights.holderThe Author(s)
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/en_US
dc.sourceBMC Medical Research Methodologyen_US
dc.source.journalissueArticle number: 17en_US
dc.source.journalvolume21en_US
dc.source.urihttps://bmcmedresmethodol.biomedcentral.com/
dc.subjectCox modelen_US
dc.subjectProportional hazardsen_US
dc.subjectTime-varying effectsen_US
dc.subjectRecurrent eventsen_US
dc.subjectPiece-wise exponential modelen_US
dc.subjectAdditive modelen_US
dc.subjectSurvival analysisen_US
dc.titleFlexible modelling of risk factors on the incidence of pneumonia in young children in South Africa using piece-wise exponential additive mixed modellingen_US
dc.typeJournal Articleen_US
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