Scientific studies often produce results that disagree. What to make of the discrepant findings? This book provides a scholarly, novel, and candid appraisal of discrepant results in mental health research. De Los Reyes draws from work in physics, medicine, history and more to make this a very engaging read. Assessment is core to all that scientists do and this book, largely focused on psychological science, has lessons that apply to science more generally as well as other domains such as government, policy, and law where assessments are used to monitor health, welfare, and social processes. The book provides a contribution without peer in how to conceptualize, use, and interpret assessments and the concrete implications that result.