Educational research outcomes frequently rely on an assumption that measurement metrics have interval-level properties. While most investigators know enough to be suspicious of interval-level claims, and in some cases even question their findings given such doubts, there is a lack of understanding regarding the measurement conditions that create nonlinear metric distortions. This dissertation aims to provide a framework that can assist researchers in thinking about the scalar properties of educational test score metrics. Following an overview of educational research studies and measurement applications that depend heavily on the interval level metric assumption, along with associated commentaries that have noted this dependence, as well as reasons to question the latent metrics produced by item response theory (IRT) models, this dissertation presents three studies: (1) an exploration of the psychological response process, particularly the proficiency-related guesses and slips in multiple-choice items, as a source of item characteristic curve (ICC) asymmetry in IRT models and thus a source of metric distortion; (2) an investigation of conditions of test multidimensionality, specifically where dimensionality correlates with item difficulty, which similarly causes nonlinear distortions of measurement metrics; and (3) an analysis of the practical impacts on vertical scaling when nonlinear metrics are not well attended to. These studies extend IRT models to incorporate nonlinear latent metrics under various conditions. The findings aim to inform the development of measurement instruments, or in some cases alternative measurement practices, that can come closer to achieving the desired interval-level properties of the measurement scale. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]