Each of these properties will be discussed later in the chapter. Validity is the extent to which an instrument measures the attributes of a concept accurately. Reliability is the ability of an instrument to measure the attributes of a variable or construct consistently. Reliability, validity, and measurement error This chapter examines the major types of reliability and validity and demonstrates the applicability of these concepts to the evaluation of instruments in nursing research and evidence-based practice. Regardless of whether a new or already developed instrument is used in a study, evidence of reliability and validity is of crucial importance.

As such, the assessment of reliability and validity is an extremely important critical appraisal skill for assessing the strength and quality of evidence provided by the design and findings of a study and its applicability to practice. Invalid measures produce invalid estimates of the relationships between variables, thus introducing bias, which affects the study’s internal and external validity. The appropriateness of instruments and the extent to which reliability and validity are demonstrated have a profound influence on the strength of the findings and the extent to which bias is present. When reading studies, you must assess the reliability and validity of the instruments to determine the soundness of these selections in relation to the concepts (concepts are often called constructs in instrument development studies) or variables under study. Nurse investigators use instruments that have been developed by researchers in nursing and other disciplines. The growing importance of measurement issues, instrument development, and related issues (e.g., reliability and validity) is evident in the Journal of Nursing Measurement and other nursing research journals. Researchers often face the challenge of developing new instruments and, as part of that process, establishing the reliability and validity of those instruments.

From either perspective, the instruments that are used in a study must be evaluated. Issues of reliability and validity are of central concern to researchers, as well as to an appraiser of research. Unless measurement instruments validly (accurately) and reliably (consistently) reflect the concepts of the theory being tested, conclusions drawn from a study will be invalid or biased and will not advance the development of evidence-based practice. Measurement of nursing phenomena is a major concern of nursing researchers. Go to Evolve at /LoBiondo/ for review questions, critiquing exercises, and additional research articles for practice in reviewing and critiquing. Contrasted-groups (known-groups) approach

Types of validity and reliability