Fundamentals of Measurement Theory

This chapter discusses the fundamentals of measurement theory. We outline the relationships among theoretical concepts, definitions, and measurement, and describe some basic measures that are used frequently. It is important to distinguish the levels of the conceptualization proces s, from abstract concepts, to definitions that are used operationally, to actual measurements. Depending on the concept and the operational definition derived from it, different levels of measurement may be applied: nominal scale, ordinal scale, interval scale, and ratio scale. It is also beneficial to spell out the explicit differences among some basic measures such as ratio, proportion, percentage, and rate. Significant amounts of wasted effort and resources can be avoided if these fundamental measurements are well understood .

We then focus on measurement quality. We discuss the most important issues in measurement quality, namely, reliability and validity, and their relationships with measurement errors. We then discuss the role of correlation in observational studies and the criteria for causality .