Each observed value is composed of the true score and measurement error. Measurement error can arise from the process of measurement itself or from factors such as carelessness, fatigue, or imprecision. When using measurement instruments or outcome measures, various sources of error can be introduced. While some sources of error, such as unclear instructions or ambiguous scoring criteria, can often be addressed during the tool’s development or design phase, observed values will inevitably contain uncontrollable measurement error. Reliability should not be understood as a binary concept (i.e., present or absent), but rather as a continuum. Thus, it is more appropriate to describe reliability as “low” or “high” depending on where it falls along this continuum.