What does CVI stand for in the context of the II calculation?

• A. Between-subject variation
• B. Analytical variation
• C. Inter-individual biological variation
• D. Intra-individual biological variation

Answer: (D)

In this context, CVI is the intra-individual biological variation—the natural fluctuation of a biomarker within the same animal over time, due to biology and physiology, not measurement error. It reflects how much a single individual’s value can vary from one measurement to the next under stable conditions. This is contrasted with inter-individual (between-subject) variation, which describes how much values differ across different animals. In calculating the index of individuality, the two relevant pieces are CVI in the numerator and CVG (the between-subject variation) in the denominator. So the index tells you how useful population reference intervals are for an individual: a small CVI relative to CVG yields a low index of individuality (values are more stable within an individual than across individuals), while a larger CVI relative to CVG yields a higher index, making population references more applicable. For example, if CVI is 5% and CVG is 20%, the index is 0.25, indicating strong individuality.