Establishing Reliability and Validity of the Criterion Referenced Exam of GeoloGy Standards EGGS

Discipline-based geoscience education researchers have considerable need for a criterion-referenced, easy-to-administer and -score conceptual diagnostic survey for undergraduates taking introductory science survey courses in order for faculty to better be able to monitor the learning impacts of various interactive teaching approaches. To support ongoing education research across the geosciences, we are continuing to rigorously and systematically work to firmly establish the reliability and validity of the recently released Exam of GeoloGy Standards, EGGS. In educational testing, reliability refers to the consistency or stability of test scores whereas validity refers to the accuracy of the inferences or interpretations one makes from test scores. There are several types of reliability measures being applied to the iterative refinement of the EGGS survey, including test-retest, alternate form, split-half, internal consistency, and interrater reliability measures. EGGS rates strongly on most measures of reliability. For one, Cronbach's alpha provides a quantitative index indicating the extent to which if students are answering items consistently throughout the test and measures inter-item correlations. Traditional item analysis methods further establish the degree to which a particular item is reliably assessing students is actually quantifiable, including item difficulty and item discrimination. Validity, on the other hand, is perhaps best described by the word accuracy. For example, content validity is the to extent to which a measurement reflects the specific intended domain of the content, stemming from judgments of people who are either experts in the testing of that particular content area or are content experts. Perhaps more importantly, face validity is a judgement of how representative an instrument is reflective of the science "at face value" and refers to the extent to which a test appears to measure a the targeted scientific domain as viewed by laypersons, examinees, test users, the public, and other invested stakeholders.