cognitive model of task performance. A cognitive model in educational measurement refers to a "simplified description of human problem solving on standardized educational tasks, which helps to characterize the knowledge and skills students at different levels of learning have acquired and to facilitate the explanation and prediction of students' performance". These cognitive skills, conceptualized as an attribute in the AHM framework, are specified at a small grain size in order to generate specific diagnostic inferences underlying test performance. Attributes include different procedures, skills, and/or processes that an examinee must possess to solve a test item. Then, these attributes are structured using a hierarchy so the ordering of the cognitive skills is specified. The cognitive model can be represented by various hierarchical structures. Generally, there are four general forms of hierarchical structures that can easily be expanded and combined to form increasingly complex networks of hierarchies where the cognitive complexity corresponds to the nature of the problem solving task. The four hierarchical forms include: a) linear, b) convergent, c) divergent, and d) unstructured. How are cognitive models created and validated? Theories of task performance can be used to derive cognitive models of task performance in a subject domain. However, the availability of these theories of task performance and cognitive models in education are limited. Therefore, other means are used to generate cognitive models. One method is the use of a task analysis of representative test items from a subject domain. A task analysis represents a hypothesized cognitive model of task performance, where the likely knowledge and processes used to solve the test item are specified. A second method involves having examinees think aloud as they solve test items to identify the actual knowledge, processes, and strategies elicited by the task,. The verbal report collected as examinees talk aloud can contain the relevant knowledge, skills, and procedures used to solve the test item. These knowledge, skills, and procedures become the attributes in the cognitive model, and their temporal sequencing documented in the verbal report provides the hierarchical ordering. A cognitive model derived using a task analysis can be validated and, if required, modified using examinee verbal reports collected from think aloud studies. Why is the accuracy of the cognitive model important? An accurate cognitive model is crucial for two reasons. First, a cognitive model provides the interpretative framework for linking test score interpretations to cognitive skills. That is, the test developer is