Mirroring the growing interest and use of statistical methods and software in education, health, and marketing, this book focuses on the statistical methods used to analyze and validate questionnaires adopted in these fields. The book features an applied approach to conducting testing and measurement in the three above-mentioned fields. The chapters build from foundations of classical measurement theory, test reliability, validity and scaling to item response theory (IRT) fundamentals, IRT for dichotomous and polytomous items, and the most recent IRT extensions.