- Profª Vanda Inácio – Pontificia Universidad Católica de Chile
- FCUL – Campo Grande – Bloco C6 Piso 4 – Sala: 6.4.30 – 15:30h
- Segunda-feira, 7 de Dezembro de 2015
A novel nonparametric regression model is developed for evaluating the covariate-specific accuracy of a continuous biological marker. Accurately screening diseased from nondiseased individuals and correctly diagnosing disease stage are critically important to health care on several fronts, including guiding recommendations about combinations of treatments and their intensities. The accuracy of a continuous medical test or biomarker varies by the cutoff threshold, c used to infer disease status. Accuracy can be measured by the probability of testing positive for diseased individuals (the true positive probability or sensitivity, Se(c), of the test) and the true negative probability (specificity, Sp(c)) of the test. A commonly used summary measure of test accuracy is the Youden index, YI=max{Se(c)+Sp(c)-1}, which is popular due in part to its ease of interpretation and relevance to population health research. In addition, clinical practitioners benefit from having an estimate of the optimal cutoff that maximizes sensitivity plus specificity available as a byproduct of estimating YI. We develop a flexible nonparametric model to estimate YI that can respond to unanticipated skewness, multimodality and other complexities because data distributions are modeled using dependent Dirichlet process mixtures. Inferences are available for the covariate-specific Youden index and its corresponding optimal cutoff threshold. The value of our nonparametric regression model is illustrated using a simulation study and data on the age-specific accuracy of glucose as a biomarker of diabetes.