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Patient-Reported Outcomes

6. Conclusion: Label What We Measure


In addition to content validity, the other psychometric properties of quality-of-life measures include:

  1. Specification of the measurement model including the instrument’s scale and sub-scale structure and the conceptual and empirical basis for combining multiple items into a single score;
  2. Reliability, including the degree to which the instrument is free from random error either by testing the homogeneity of content on multi-item tests with internal consistency evaluation or testing the degree to which the instrument yields stable scores over time;
  3. Construct, criterion, and predictive validity wherein the logical relationships among different measures are examined;
  4. Responsiveness or ability of the measure to assess change over time when real change has occurred (longitudinal construct validation); and
  5. Interpretation of the effect size, or the degree to which one can assign qualitative meaning to an instrument’s quantitative scores (Scientific Advisory Committee, Medical Outcomes Trust, 2002; Patrick et al., 2007).

Note that rigorous adherence to standards of measurement of PROs is as important as finding the most appropriate label for what is being measured.