What makes a measurement instrument valid and reliable?
Introduction
Different measurement instruments are used in trauma. They vary from fracture classification systems, X-rays, laboratory tests, patient-reported questionnaires, to physical examination, and are used for different purposes, such as diagnosis, prognosis, long term follow up or evaluation of an intervention. High quality instruments provide a useful tool for our clinical and research purposes. The quality of some instruments is well documented, but for many it is still unclear.
To determine whether an instrument has high quality, measurement properties such as reliability and validity need to be assessed.11 The best way to determine this is by systematically reviewing the literature on its measurement properties using good criteria.27 Since the quality of the instrument directly relates to the quality of the studies in which the measurement properties were evaluated, standardized criteria are also needed to assess the quality of these studies.27
Recently, these standardised criteria were published by the COSMIN group. COSMIN stands for COnsensus-based Standards for the selection of health Measurement INstruments.14, 16 They developed a manual and a checklist to evaluate the methodological quality of studies on measurement properties. In addition, they defined the terminology and definitions of measurement properties, as well as the position of each measurement are described in a taxonomy.15 All were developed in a multidisciplinary, international Delphi-study in which experts from all over the world participated, and can be found on the COSMIN website (www.cosmin.nl).14, 15, 16
The purpose of this paper is to describe the key measurement properties of a measurement instrument as defined by the COSMIN group. Interpretation of the different measurement properties will be explained by using examples of measurement instruments utilized in trauma. This paper's emphasis is on learning how to apply these criteria when evaluating a measurement instrument on its quality.
After reading this paper, the reader
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should know that the quality of a measurement instrument is described by three quality domains: reliability, validity and responsiveness
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should know that the quality domain reliability contains three measurement properties: internal consistency, reliability and measurement error
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should know that the quality domain validity contains three measurement properties: content validity, construct validity and criterion validity
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should know how to evaluate or assess the quality of a measurement instrument on reliability and validity.
Section snippets
Three quality domains: reliability, validity and responsiveness
The quality of a measurement instrument is described by three quality domains. These are reliability, validity and responsiveness. This paper will only address the first two domains: reliability and validity.
Summary
Different measurement instruments are used in trauma. Before considering using or implementing a measurement instrument into a clinical or research setting, one should evaluate its quality. According to the COSMIN guidelines, the quality of a measurement instrument is described by three quality domains: reliability, validity and responsiveness. Reliability contains the measurement properties internal consistency, reliability and measurement error, whereas validity contains content validity,
Conflicts of interest
The authors declare no conflict of interest, real or perceived, financial or nonfinancial.
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