Book excerpt: The intention of this book is to provide training officials - working in law enforcement, courts, adult corrections, juvenile justice, child and family welfare, fire safety, emergency medical care, and related agencies - with valid mechanisms for assessing the degree to which trainees actually acquire the knowledge and skills required to effectively perform duties that can be complex and challenging, in order to determine which trainees will and will not be formally credentialed to perform work. This book addresses the current void in the literature on the topic and to encourage increased attention to the question of whether tools being used to assess knowledge and skills acquired from training conform to scientifically established standards of validity. The meticulous efforts of the authors have produced a solid basis for application through comprehensible and concrete theoretical principles. The aim of the book is to show how to perform validation of training assessment instruments by actually doing so and by addressing the central issues that warrant consideration in the process. The book begins with background information that is important to the authors' research on the validity of tests used in policed training. After providing the background in the first three chapters, the following four chapters describe and present the findings of their validation study of police academy testing. The last chapter draws conclusions about the validity and reliability of the instruments that were studied and by examining the implications of their research for future efforts to validate tests in justice and safety training contexts. The book also contains appendices that present data to support the conclusions and also include methods and instruments developed during the authors' research.