Defining aphasia: Content analysis of six aphasia diagnostic batteries.

Clear operational definitions of constructs are necessary to ensure that research findings are meaningful and interpretable. In the field of aphasiology, aphasia is often defined to the effect of "aphasia is an acquired language disorder often due to brain injury that affects expressive and receptive language." To contribute to our understanding of the construct of aphasia, we conducted a content analysis of six diagnostic aphasia tests: the Minnesota Test for the Differential Diagnosis of Aphasia, the Porch Index of Communicative Ability, the Boston Diagnostic Aphasia Examination, the Western Aphasia Battery, the Comprehensive Aphasia Test, and the Quick Aphasia Battery. These chosen tests have historical prominence, with several in regular clinical and research use today. We hypothesized that the content of the aphasia tests should be very similar since they all purport to identify and characterize (if present) aphasia, with recognition that there may be some subtle differences in test content stemming in large part to epistemological differences in the test makers' views of aphasia. Instead, we found predominantly weak Jaccard indices, a similarity correlation coefficient, between test targets. Only five test targets were found in all six aphasia tests: auditory comprehension of words and sentences, repetition of words, confrontation naming of nouns, and reading comprehension of words. The qualitative and quantitative results suggest that the content across aphasia tests may be more disparate than expected. We conclude by discussing the implication of our results for the field, including the importance of updating, if necessary, the operational definition of aphasia through conversation with a broad audience of interested and affected people.