Original article
Measuring change over time: Assessing the usefulness of evaluative instruments

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Abstract

Reliability, the ratio of the variance attributable to true differences among subjects to the total variance, is an important attribute of psychometric measures. However, it is possible for instruments to be reliable, but unresponsive to change: conversely, they may show poor reliability but excellent responsiveness. This is especially true for instruments in which items are tailored to the individual respondent.

Therefore, we suggest a new index of responsiveness to assess the usefulness of instruments designed to measure change over time. This statistic, which relates the minimal clinically important difference to the variability in stable subjects, has direct sample size implications. Responsiveness should join reliability and validity as necessary requirements for instruments designed primarily to measure change over time.

References (23)

  • B Kirshner et al.

    A methodologic framework for assessing health indices

    J Chron Dis

    (1985)
  • JM Lachin

    Introduction to sample size determination and power analysis for clinical trials

    Controlled Clin Trials

    (1981)
  • WA Nicewander et al.

    Dependent variable reliability and the power of statistical tests

    Psychol Bull

    (1978)
  • WA Nicewander et al.

    Reliability of measurement and the power of statistical tests: some new results

    Psychol Bull

    (1983)
  • EG Carmines et al.

    Reliability and Validity Assessment

    (1979)
  • BJ Winer

    Statistical Principles in Experimental Design

  • JP Guilferd

    Fundamental Statistics in Psychology and Education

  • MS Kramer et al.

    Clinical biostatistics LII: the biostatistics of concordance

    Clin Pharmacol Ther

    (1981)
  • American Psychological Association: Standards for Educational and Psychological Tests. American Psychological...
  • GW Maslany et al.
  • JC Nunally

    Psychometric Theory

    (1978)
  • Cited by (0)

    This work has been partially supported by the Medical Research Council: by St Joseph's Hospital Foundation. Hamilton. Ontario: and by the Ontario Ministry of Health. Dr Guyatt is a career scientist of the Ontario Ministry of Health.

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