Despite warnings that the field of learning disabilities (LD) must address the issue of population heterogeneity, the LD research community still lacks operational definitions of specific learning disabilities as well as a systematic approach for reporting sample characteristics. Recently, however, a definition of dyslexia has been proposed that might signal a significant advance. This article builds on this definition of dyslexia by: (a) reintroducing the concept of marker variables, (b) proposing a strategy for developing an updated marker variable system, (c) presenting a preliminary working set of dyslexia marker variables, and (d) calling for the eventual adoption of this or similar marker variable systems to facilitate future research efforts.
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