Use of Zero-Inflated Mixture Models to Compare Antigen-Specific IgE Levels Among Subpopulations of Atopic Dermatitis Patients

• Activity Number: 111
• Type: Contributed
• Date/Time: Monday, August 3, 2009 : 8:30 AM to 10:20 AM
• Sponsor: Biometrics Section
• Author(s): Daniel Zaccaro*+ and Brian Armstrong and Natalija Novak and Thomas Bieber
• Companies: Rho, Inc. and Rho, Inc. and University of Bonn and University of Bonn
• Keywords: zero-inflated models ; atopic dermatitis ; excess zero models

Abstract

Allergen-specific IgE antibody levels exhibited an excess of values below the lower detection limit (34-85% of patients) and values above the upper detection limit (up to 30% of patients), a challenge when comparing IgE among subgroups of atopic dermatitis patients. Zero-inflated log-normal models, accounting for left- and right-censoring and a "point mass" component, were evaluated using AIC along with ordinary least squares (OLS) regression to examine subgroup differences in IgE levels. For most antigens, zero-inflated models with left-censoring provided a better fit than OLS or left-censoring alone models. Zero-inflated models with both Bernoulli and log-normal components suggested differences in "point mass" proportions as well as quantitative differences, using all IgE data without imputation of censored values. Power and potential bias were assessed with simulation studies.