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Revisiting Classification and Identification

In his invitation to contribute to this special issue, LDQ Editor David Scanlon suggested I discuss issues of classification and identification. I am pleased to do that as I think some of the continuing controversies about learning disabilities (LD) are related to those topics. More specifically, I suggest that many problems have to do with confusion between the two. Despite years of effort and an extraordinary increase in the number of individuals considered as having LD, we continue to grapple with vagaries and inconsistencies in classification, definition, and identification. We continue to face critical challenges about "what is LD? "who is LD and who isn't' LD?" and "how do we know?" Our problems are in part related to a lack of clear boundaries between LD and other conditions. They also relate to definitions that serve political, legislative, advocacy, or intervention needs as well as research or "scientific" purposes. To muddle the problem further, classification problems are compounded by limited and often inadequate or inappropriate operational methods of identification. Problems and confusions in classification and identification are not new, and they are not limited to the field of LD. Over 40 years ago, Zigler and Phillips (1961) published a seminal article titled "Psychiatric Diagnosis: A Critique," in which they examined problems in classification and identification of psychiatric conditions. For those of us in the LD field the article is as relevant today as it was in psychiatry then. Zigler and Phillips argued that "Reduced to essentials, diagnostic classification involves the establishment of categories to which phenomena can be ordered" (p. 608). Such efforts result in a map or a taxonomy that systematically describes a field. In this sense, classification is fundamental in organizing any field, and LD is no exception. In contrast to classification, identification refers to the assignment of individuals or exemplars to classification categories and, thus, relates to operational decisions, methods, and measures. Who is included and who is not included as LD is a function in part of what measures, procedures, and criteria are used. Which psychometric tests? Where are the cutoff points? How large must a discrepancy be? As fisherman have long known, the size of the net affects the size of the fish that are netted. Zigler and Phillips argued that three criteria were essential in determining the adequacy and utility of a classification system: homogeneity, reliability, and validity. In their analysis, homogeneity refers to the similarity (or lack of) of those included in a category. Reliability refers to the degree of agreement when placing individuals in categories. Finally, validity refers to how well category membership informs prognosis or treatment. Applying these criteria to classification in LD, consider first the question of homogeneity. There are different definitions of LD and there have been changes over the years (see Kavale & Forness, 2000, for discussion). The LD classification is defined as much by what it isn't as by what it is, and it is accompanied by a long list of exclusions, for example, learning problems due to generalized cognitive limitations, to social/cultural conditions, or to instructional inadequacies. The result is a broad band of learning problems gathered under the LD rubric, thus posing a challenge to homogeneity. In Zigler and Phillips' discussion, reliability raises the question of consistency of identification. Specifically, is there agreement about who should be included or who should be excluded from the category? In LD, decision rules about inclusion and exclusion differ widely, and identification may be influenced by a number of extraneous conditions. For example, where you live and go to school and your cultural and familial status, in addition to the nature and degree of your learning problem, may determine whether or not you will be identified as LD. …