Symposium on Quality of Life in Cancer Patients
Group vs Individual Approaches to Understanding the Clinical Significance of Differences or Changes in Quality of Life

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This article focuses on the traversing of group and individual levels of quality-of-life data. A deductive approach is used to address the extent to which group data can be used to estimate clinical significance at the individual level. An inductive approach is used to evaluate the extent to which individual change data can be brought to the group level to define clinical significance. Both approaches have benefits and drawbacks. This article addresses how clinical significance can be defined for an individual when the threshold for meaningfulness is drawn from group data. It also addresses the condition under which one can use the same threshold difference for group vs individual differences or changes. A sample inductive approach explores the means to identify a clinically significant result or change, with use of insights from cognitive psychology. In most deductive approaches, the identification of a clinically significant difference or change requires identification of a criterion (or at least an interpretable anchor) against which the significance of a change in respondent score is compared.

Section snippets

CRITERIA FOR CLINICAL SIGNIFICANCE

Unless one is willing to rely exclusively on distribution-based estimates of magnitude (eg, effect size), the identification of a CSD or clinically significant change requires one to identify a criterion (or at least an interpretable anchor) by which the significance of a change in respondent score is compared. One of the essential problems of patient-based health outcome measures, such as QOL indicators, is the position that a subjective perception of QOL or perceived health does not have a

Instrumentation and Measurement Standards

Instrumentation and measurement standards have been proposed to determine the usefulness of a particular instrument. There are several ways in which an instrument is potentially useful. It may be useful for individual diagnosis, group comparisons, or both. An instrument useful for individual diagnosis is rarely inappropriate for group comparisons; however, many instruments useful for group comparisons are inappropriate for individual diagnosis. Furthermore, within the realm of useful for group

Deductive Approaches

Still unresolved is the question of how group-level test results may be applied to individuals. Related is the question regarding the consequences of identifying an individual patient's status or change based on group data in terms of clinical meaningfulness. This topic can be discussed within the scenario of field studies, in which group-to-individual comparisons are necessary. One scenario could be to deductively interpret the results for an individual patient enrolled in a clinical trial

A COGNITIVE APPROACH TO CSD

Using the common deductive approach to clinical significance, group data are frequently used to provide an average estimate of an individual's view of CSD. In contrast, a cognitive perspective takes the inductive approach and asks how an individual judges CSD, and then uses this information to provide a model of a group measure CSD. When patients wish to assess the significance of a change in their health status, they usually compare and value some baseline estimate with their current health

CONCLUSIONS

Measuring QOL change is complex. If patients say they feel better from one assessment to the next (subjective anchor), they often, but not always, give higher QOL ratings in that second assessment. Similarly, patients who globally say they are doing worse at subsequent assessments tend, on average, to report worsened condition on an item-by-item basis. However, there is also substantial variability in the reporting of scores, including some patients who say they are better and report themselves

TOPICS FOR FURTHER STUDY

Further research is necessary to examine the extent to which individual and group criteria for clinical significance agree with one another. Currently, one is required to traverse the two with a degree of faith. It would also be useful to determine the conditions and circumstances that predict good fit between individual and group criteria. This could be investigated by assessing, in an epidemiological study or a clinical trial, multiple anchors for each individual and then comparing individual

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    This project was supported in part by Public Health Service grants CA25224, CA37404, CA15083, CA35269, CA35113, CA35272, CA52352, CA35103, CA37417, CA63849, CA35448, CA35101, CA35195, CA35415, and CA35103.

    Individual reprints of this article are not available. The entire Symposium on the Clinical Significance of Quality-of-Life Measures in Cancer Patients will be available for purchase as a bound booklet from the Proceedings Editorial Office at a later date.

    A complete list of other Clinical Significance Consensus Meeting Group contributors to this article appears at the end of the article.

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