title: Accommodation of additional non-randomly sampled cases in a study of Helicobacter pylori infection in families.
abstract: Epidemiological studies with two-stage designs typically gather information about some covariates from all study subjects in the first sampling stage, while additional data from only a subset of the subjects are collected in the second sampling stage. Appropriate analysis of two-stage studies maintains validity and can also improve precision. We describe an application of a weighted likelihood method, mean-score logistic regression, to accommodate data from a cross-sectional study of Helicobacter pylori infection in children, where the study sample was enriched with additional non-randomly sampled cases. The present work exemplifies how careful analysis of epidemiological data from complex sampling schemes can adjust for potential selection bias, improve precision and enable a more complete investigation of factors of interest. Our results highlight the importance of H. pylori infected mothers and siblings as risk factors for the infection in children in Sweden.
authors.affiliation: Department of Medical Epidemiology and Biostatistics (MEB), Karolinska Institutet, Stockholm, Sweden.
authors.forename: Mårten
authors.initials: M
authors.lastname: Kivi
authors.forename: Anna L V
authors.initials: AL
authors.lastname: Johansson
authors.forename: Agus
authors.initials: A
authors.lastname: Salim
authors.forename: Ylva
authors.initials: Y
authors.lastname: Tindberg
authors.forename: Marie
authors.initials: M
authors.lastname: Reilly
mesh_terms: D002648:Child; D003430:Cross-Sectional Studies; D003627:Data Interpretation, Statistical; D016021:Epidemiologic Studies; D005190:Family; D016481:Helicobacter Infections / Q000453:epidemiology*; D016480:Helicobacter pylori / Q000472:pathogenicity; D006801:Humans; D016015:Logistic Models; D018579:Patient Selection; D013548:Sweden / Q000453:epidemiology