ABSTRACT
This chapter discusses general methodological issues relevant to field studies of vaccine effectiveness. These include: the choice of case definitions; biases due to misclassification of disease and vaccination status, and inclusion of prior cases; confounding bias including indication bias and healthy vaccine bias; bias-indicator studies; and the choice of epidemiologic measures (risks or rates) to calculate vaccine effectiveness and their impact on vaccine effectiveness. The chapter ends with some brief remarks about modelling frameworks. All of these issues are relevant to the specific designs of vaccination effectiveness studies that are discussed in Chapters 14 to 16.
