Any individual message an ad, speech, news story, school curriculum, or remark made in a conversation has distinct properties and effects. The study of these effects is a primary task of communication research. In this fascinating and controversial new work, Sally Jackson critiques the methodology behind generalized claims about message effects and lays the groundwork for a methodological alternative. Central to this is the notion that methodology must be tailored to the special characteristics of a field's objects of study. To shape the methodology within the particular case of message research, it is necessary to examine the kinds of claims the researcher wishes to make and the threats to validity that affect such claims. This book will be of value to experimental social scientists in all fields concerned with language and messages including communication, social psychology, education, journalism, and advertising. It also serves as a supplementary text for graduate and advanced undergraduate courses in experimental design, and is a helpful guide for instructors who wish to focus on the substantive problems or research in their design and analysis courses.