What is the MDC for the KOOS?

• A. 2-4 for each subscale
• B. 8-10 for each subscale
• C. 12-14 for each subscale
• D. 15-20 for each subscale

Answer: (B)

Minimal detectable change (MDC) is the smallest amount of change that exceeds the instrument’s measurement error at a chosen level of confidence. For the KOOS, each subscale runs 0–100, with higher scores indicating better status. MDC is derived from the standard error of measurement, which depends on the subscale’s reliability and variability, and is commonly reported for KOOS subscales around 8–10 points at 90% confidence. This means a change of about 8–10 points on any KOOS subscale is the threshold at which you can be confident that true change has occurred, not just measurement noise. Smaller changes (2–4 points) are usually within error, while larger ranges (12–14 or 15–20) reflect more substantial change than the minimal detectable amount. Therefore, 8–10 points per subscale is the best choice.