Joint Response Models PDF
By:Stephen Paul Phillips
Published on 2002 by
The decline in caries prevalence and changed distribution, the increased exposure to fluoride - through water supplies and via rinses, tablets, and topical applications, and the need to test products using 'fluoride based' controls for undisputed ethical reasons, have all complicated clinical trials in recent times. Consequently, much larger sample sizes have been required to detect statistically significant differences between products resulting in large increases in costs. This thesis proposed the use of a joint response model approach in the analysis of data from three-year caries clinical trials. Models were developed for measuring the effectiveness of fluoride dentifrices utilizing all examination data within the trial where the unit of observation was the subject's tooth surface. The joint response models (MODEL _A and MODEL_B) consisting of logit model and proportional odds model (POM) components at each examination were fitted to a particular three-year caries clinical trial, with MODEL_B incorporating the ordinal nature of the categorical response caries variables [a response variable at each examination t (t=1:3)] utilizing further available information. Here logit and proportional odds model (POM) components were used but other models might be tried in future research. Important parameter estimates, and therefore explanatory variables, were identified at each examination through their statistical significance, and in an overall sense, for both MODEL_A and MODEL-B. The results obtained were similar to previously applied methods in relation to most explanatory variables. Because the joint response models were applied to a tooth surface level dataset, which has observations that are not independent, methods had to be developed that accounted for this problem - the grouped jackknife methodology was used. Drawing firm conclusions based on the analysis of a single dataset is not advisable. The methodology developed in this thesis needs to be applied to several different caries clinical trials. If data is unavailable, simulation is another option. Only then can firm conclusions be reached on whether or not sensitivity might be improved by using the joint response model approach. If improved sensitivity were to be established it might be that fluoride dentifrices could be compared using fewer subjects and thus reduce costs associated with these clinical trials.
This Book was ranked at 38 by Google Books for keyword Caries.
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