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As we approached the revision of this text for the third edition, we realized that the prevailing paradigms of clinical research in rehabilitation and medicine had continued to evolve over the past 10 years, and that we had to address several important changes in the research landscape. Probably the most notable of these changes is the emphasis on evidence-based practice (EBP) that has become central to all of health care. The World Health Organization's adoption of the International Classification of Functioning and Disability (ICF) has created a new vocabulary that is being integrated into research and practice across disciplines. Questions related to diagnostic accuracy and clinical decision making are prominent in research literature, and phrases like "responsiveness," "minimally important change" and "number needed to treat" are becoming essential to EBP. Attitudes about clinical research have emphasized the responsibility of every clinician to better understand how to apply evidence to patient care, and the gaps in our research knowledge have become more evident as we often search for answers that are not there.

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This book has served a variety of audiences in research, professional education and clinical practice. It continues to be directed toward those in physical therapy, occupational therapy, speech therapy, nursing, medicine, exercise physiology, and public health, as well as other disciplines concerned with questions of health and health care. The book will remain a text for courses in research and critical inquiry, as well as a comprehensive reference for clinicians and researchers who are committed to evidence- based practice.

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We have included varied levels of detail in design and statistics to meet the diverse needs of those who use this text. Instructors are urged to consider which portions of the text are relevant for their students, and not to expect to use it all in their courses. Students will find it user-friendly as they learn concepts and principles of research, and will keep it is a reference as they grow in their professional role. Those who are engaged in research activities or advanced education will be able to utilize the more detailed portions as they explore research questions. And clinicians will be able to apply these principles to their clinical decision making.

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The application of evidence-based practice to health care requires an understanding of design and analytic methods. Our text is not going to provide the answers to clinical questions for practice—that must be left to journal articles and clinical textbooks, and to those who mentor students and clinicians, who will ask the right questions. Our contribution is to provide the foundations that are necessary for finding and interpreting research evidence. Clinicians must provide the experience and knowledge to apply the research to their practice.

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Although the general organization of the book has not changed, several additions have been incorporated into this edition to provide a contemporary framework for clinical research. Part I covers the basic concepts of research, including a discussion of theory and ethical principles. In this section we introduce important contexts for research related to models of health and evidence-based practice. Part II focuses on measurement, including a comprehensive examination of reliability and validity. Part III presents the broad scope of experimental, exploratory and descriptive research approaches, including a new chapter on systematic reviews and meta-analysis.

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Part IV of the text is devoted to the application of statistical procedures, from descriptive to multivariate approaches. This section now contains expanded content related to clinical decision making, including likelihood ratios, pretest and posttest probabilities, minimally important change and number needed to treat. We continue to focus on the conceptual foundations of statistics, although calculations are provided for those who desire that level of detail. We use the format for SPSS in presenting output, but with explanations that we trust will allow integration with other statistical packages.

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Part V focuses on processes of research and communication, including an expanded chapter on searching the literature, development of proposals, presentation of research, and critical appraisal of published literature. Appendices provide tables of reference for statistical procedures, a newly designed algorithm for choosing statistical approaches for analysis, examples of power analysis for various designs, methods of transforming data, and a sample informed consent form.

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Prentice Hall has provided a wonderful opportunity to share information related to all sections of the book on their companion website, which can be accessed at www.prenhall.com/portney. We hope you will find this a helpful addition to the text, especially for those who use it for teaching purposes.

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As the health care environment evolves, we will always anticipate new directions and priorities for clinical research. Therefore, this work will always be in progress. We are proud to be part of the larger health care research and clinical communities that are clearly dedicated to the pursuit of new knowledge and the application of evidence to improve patient care. We look forward to the continued journey with all of you.

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