Patient-Reported Outcomes

6. Conclusion: Label What We Measure

Table 3

Condition Clinical Signs & Symptoms  Aspects of Life Affected 
Acne An inflammatory skin condition characterized by superficial skin eruptions around hair follicles. Major Symptoms: Skin rash or lesion on the face, neck, chest, shoulders and back / comedones (whiteheads or blackheads) / pustules / cysts / papules / nodules / inflammation around the skin eruptions
  • Going to social events like dances
  • Feeling depressed and lonely
  • Itching, redness, raw skin (symptoms)
  • Difficulty finding romantic partners
Osteoarthritis Degeneration of the cartilage that lines the joints. Major Symptoms: pain/tenderness, swelling, creaking, stiffening of affected joints, weakness & shrinkage of surrounding muscles due to lack of use (because of pain), enlarged & distorted joints
  • Difficulty bending, kneeling, stooping
  • Difficulty walking up hill
  • Depressed
  • Difficulty turning over in bed

Regardless of how items are arranged or how domains are grouped, it is generally agreed that the content validity of PROs can be judged only by the persons or populations being assessed. Thus, the extent to which the domain of interest is comprehensively sampled by the items or questions in the measure can only be judged by representatives of the target population. If the target population is unable to speak for themselves, proxy judgments are sometimes considered acceptable, particularly if supported by rigorously controlled observational studies with inter-rater reliabilities. Before assuming that people cannot speak for themselves, however, they should be asked and every effort should be made to communicate with them directly. Proxy responses are not PROs.

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.