title: A mixture model with detection limits for regression analyses of antibody response to vaccine.
abstract: Antibody concentration values as determined by quantitative assays often are left-censored due to detection limits or limits established for purpose of specificity. Standard analyses which assume the data arise from a single lognormal response distribution may not be appropriate, when more observations are censored than would be expected under such a model. Interference from maternal antibodies due to vaccination at an early age, for example, could result in a high proportion of nonresponders to vaccine. A mixture model consisting of a censored lognormal distribution and a point distribution located below the detection limit is proposed for such situations. Antibody data from a study of measles vaccine are used to illustrate the utility of this approach and the interpretation of the model parameters.
authors.affiliation: Department of International Health, Johns Hopkins University, School of Hygiene and Public Health, Baltimore, Maryland, USA.
authors.forename: L H
authors.initials: LH
authors.lastname: Moulton
authors.forename: N A
authors.initials: NA
authors.lastname: Halsey
mesh_terms: D000914:Antibodies, Viral / Q000097:blood; D000917:Antibody Formation; D001699:Biometry / Q000379:methods*; D017321:Clinical Trials, Phase I as Topic / Q000706:statistics & numerical data; D017322:Clinical Trials, Phase II as Topic / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007112:Immunity, Maternally-Acquired; D007223:Infant; D016013:Likelihood Functions; D016014:Linear Models; D008297:Male; D008458:Measles Vaccine / Q000009:adverse effects / Q000276:immunology; D008954:Models, Biological; D015233:Models, Statistical; D011247:Pregnancy; D012449:Safety; D012727:Sex Characteristics; D014612:Vaccines / Q000276:immunology*
chemical_list: D000914:Antibodies, Viral; D008458:Measles Vaccine; D014612:Vaccines