An SDI value of 2.5 indicates poor performance.

• A. True
• B. False
• C. Not applicable
• D. Cannot determine

Answer: (A)

SDI expresses how far a lab’s result is from the peer group mean, measured in units of the peer group standard deviation. Values within about ±2 standard deviations are generally considered acceptable. A value of 2.5 means the result is 2.5 standard deviations away from the peer mean, which lies outside the acceptable range and signals poor performance. The positive sign simply indicates the result is higher than peers, but the key point is that 2.5 shows a notable deviation needing investigation.