referenssipiirrettä

A referenssipiirre is a concept primarily used in the field of psychometrics and statistical modeling, particularly in the analysis of item response theory (IRT). It refers to a specific item on a test or questionnaire that is administered to all participants and serves as a stable benchmark for comparison. The performance of other items on the test, or the ability levels of individuals, are then calibrated relative to this reference item.

The primary purpose of a referenssipiirre is to anchor the measurement scale. By including a consistently performing item, researchers can ensure that different test administrations or different sets of items are on the same underlying scale. This is crucial for longitudinal studies, where the same individuals are measured at different times, or when comparing results from different versions of a test. Without a referenssipiirre, changes in scores could be due to genuine changes in ability or due to shifts in the difficulty or characteristics of the items themselves.

In essence, the referenssipiirre acts as a fixed point, allowing for the accurate estimation of other parameters. Its characteristics, such as difficulty and discrimination, are assumed to be known or reliably estimated. When new items are introduced or when tests are adapted, their parameters are estimated in relation to the established referenssipiirre. This process is known as equating. The selection of a good referenssipiirre is therefore important, as it should be an item that is not too easy or too difficult, and that differentiates well between individuals of varying ability levels.