In computing an analyte's index of individuality, which components must be considered?

• A. Within-individual CV, between-individual CV, and analytical CV.
• B. Between-lab CV, external CV, and sample CV.
• C. Mean and standard deviation only.
• D. Sensitivity and specificity.

Answer: (A)

The index of individuality compares how much an individual’s results vary over time to how much the results vary between different people. To compute it correctly you need the within-subject variability (how a single person’s values fluctuate), the between-subject variability (how much people differ from each other), and the analytical variation (the measurement imprecision) because the observed fluctuations within a person include both true biological variation and assay error. If you only use the raw within-subject variation without accounting for analytical error, you may misestimate the true biological variation and misinterpret the index. So, all three components—within-individual CV, between-individual CV, and analytical CV—are essential.