Which scale has an MDC of 1 unit?

Which scale has an MDC of 1 unit?

• A. Tegner Activity Scale
• B. LEFS
• C. SF-36
• D. ACL-RSI

Answer: (B)

Minimal detectable change is the smallest amount of change that exceeds measurement error at a given confidence level. It shows when a change you observe reflects real improvement or decline, not just random variation. The Lower Extremity Functional Scale fits this idea best here because it has a high level of reliability and a relatively small standard error of measurement. It’s a 20-item questionnaire with each item scored 0–4, giving a total score from 0 to 80. Because the items are consistent and the overall measurement error is small, the calculated MDC for an individual can be as low as about 1 point on the total score. In practical terms, a patient improving by around 1 point is likely experiencing true improvement rather than noise. The other scales span broader domains and have greater variability or larger score ranges, which tends to yield a larger MDC and make such tiny changes unreliable as real change. It’s also important to note that MDC is about detecting any real change, whereas the minimum clinically important difference (MCID) is about changes that patients perceive as meaningful, and MCID is usually larger than the MDC.

Minimal detectable change is the smallest amount of change that exceeds measurement error at a given confidence level. It shows when a change you observe reflects real improvement or decline, not just random variation.

The Lower Extremity Functional Scale fits this idea best here because it has a high level of reliability and a relatively small standard error of measurement. It’s a 20-item questionnaire with each item scored 0–4, giving a total score from 0 to 80. Because the items are consistent and the overall measurement error is small, the calculated MDC for an individual can be as low as about 1 point on the total score. In practical terms, a patient improving by around 1 point is likely experiencing true improvement rather than noise.

The other scales span broader domains and have greater variability or larger score ranges, which tends to yield a larger MDC and make such tiny changes unreliable as real change. It’s also important to note that MDC is about detecting any real change, whereas the minimum clinically important difference (MCID) is about changes that patients perceive as meaningful, and MCID is usually larger than the MDC.