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Recurrent event analysis
- Andreas Wienke (26 October 2009)
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Andreas Wienke, Biostatistician University Halle-Wittenberg, 06097 Halle, Germany
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Dear Sir, Donaldson et al. (2009) presented a very interesting review of interventions to prevent falls. I would like to congratulate Donaldson and colleagues to their nice and stimulating research. However, I have one important comment on the article. The authors check in their article the use of appropriate statistical methods in the analysis of interventions to prevent falls. They conclude that fewer than one third of the considered papers used appropriate statistical methods for analysis of recurrent event data. Donaldson et al. classify three approaches as appropriate models for the analysis of recurrent event times based on Kuramoto et al. (2008): negative binomial regression, the Anderson-Gill model and the WLW marginal model. I would like to point out that the negative binomial regression model is in fact a frailty model with gamma distributed frailty and exponential baseline hazard function. This is a rather restricted model, assuming a constant recurrent event rate over time. It remains unclear why the authors restrict to this model in their review instead of allowing for general frailty models (Duchateau and Janssen, 2008). In this class of models similar to the Cox proportional hazards model no parametric assumption about the baseline hazard function is necessary. Furthermore, additional to the gamma other frailty distributions can be used. These models are well designed for the analysis of recurrent event time data (Duchateau et al. 2003), including total follow-up time as well as gap time model variants. Software for frailty models is free available in form of SAS macro's and R routines. Based on this fact it remains unclear how many analyses in the review are wrongly classified as not appropriate because of the restriction to the negative binomial regression instead of considering frailty models. Sincerely yours Andreas Wienke (andreas.wienke@medizin.uni-halle.de) References: Duchateau, L., Janssen, P., Kezic, I., Fortpied, C. (2003) Evolution of recurrent asthma event rate over time in frailty models. Applied Statistics 52, 355-363 Duchateau, L., Janssen, P. (2008) The Frailty Model. Springer, New York Kuramoto, L., Sobolev, B.G., Donaldson, M.G. (2008) On reporting results from rando- mized controlled trials with recurrent events. BMC Medical Research Methodology 8, 35 Conflict of Interest:None declared |
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