A Marker System for Describing Learning-Disability Samples
This chapter focuses on sampling issues in the study of learning disabilities. The content is based on the observation that many of the limitations in interpreting the data-based literature on this topic stem from confusions and inconsistencies in subject selection criteria and practices. The effect of unknown sampling differences is the proliferation of an increasingly large number of separate studies that do not allow generalization and that offer only limited theoretical inferences. Ambiguities and unknowns in research samples necessarily restrict inferences from one study to another and prevent the aggregation of data from different research groups.