What is also known as Standard Deviation Index or SDI?

• A. P-Value
• B. Z-Score
• C. R-Squared
• D. Confidence Interval

Answer: (B)

The Standard Deviation Index is a standardized score that tells you how far a result is from the target value in units of standard deviation. In proficiency testing, this is effectively a Z-score: you take the difference between the observed result and the target (mean) value and divide by the peer group’s standard deviation. This makes outcomes on different tests comparable and shows how unusual a result is relative to peers.

P-values measure the probability under a null hypothesis, not distance from a target. R-squared reflects how much variance a model explains, not a standardized deviation from a target. Confidence intervals give a range where the true parameter likely lies, not a single standardized distance.