Quality of Life in Age-Related Macular Degeneration - CNIB

· Test­retest reliability: The extent to which scores remain stable over
time when no change has occurred (i.e. when there has been no
change in vision, no treatment for MD or rehabilitation).
· Construct validity: Hypotheses concerning the relationship of
questionnaire scores to other measures (such as VA or contrast
sensitivity) are tested. Ability to discriminate between levels of disease
severity (e.g. between people who are registered blind, partially sighted
or not registered) is important, particularly for a visual function measure,
which would be expected to correlate strongly with disease severity
· Responsiveness: Sensitivity to real change over time (e.g. deterioration
in VA or contrast sensitivity)
· Interpretability: The extent to which change scores can be interpreted
and explained
In addition to these psychometric properties, the burden placed upon
respondents should be considered (length of questionnaire, complexity of
language, relevance of the questions) and that on administrators 45 . Where
questionnaires are designed in one language and translated into other
languages, linguistic validation is required, including cultural adaptation where
needed 46 . Forward and backward translations are necessary (preferably
reviewed by the questionnaire author) to ensure that the translations have not
introduced semantic discrepancies. Clinician review can be helpful and
cognitive debriefing interviews with people who have MD are needed to
ensure that the translated items and instructions are understood as intended.
Psychometric evaluation of each language version is necessary, at least on
first use, before analysing data from multiple languages as one dataset.
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