What is a key difference between GMFM-88 and GMFM-66?

What is a key difference between GMFM-88 and GMFM-66?

• A. GMFM-66 has more items than GMFM-88.
• B. GMFM-66 is unrelated to GMFM-88.
• C. GMFM-66 is another test entirely.
• D. GMFM-66 is a Rasch-calibrated version with 66 items derived from GMFM-88; GMFM-88 contains more items.

Answer: (D)

A key difference is that the GMFM-66 is a Rasch-calibrated subset of the original 88-item GMFM. It uses 66 items that were selected to fit a Rasch measurement model, and the resulting score is a single interval-level measure of gross motor function. This allows more precise tracking of change over time and easier comparison across children and settings. The GMFM-88, by contrast, contains 88 items and is typically scored in a more ordinal way across five domains, without the same single-interval scale. So the 66-item form derives from the 88-item form and adds the Rasch-based scoring, giving a unified, interval-scale score, while the 88-item form provides more items but with ordinal interpretation.

A key difference is that the GMFM-66 is a Rasch-calibrated subset of the original 88-item GMFM. It uses 66 items that were selected to fit a Rasch measurement model, and the resulting score is a single interval-level measure of gross motor function. This allows more precise tracking of change over time and easier comparison across children and settings. The GMFM-88, by contrast, contains 88 items and is typically scored in a more ordinal way across five domains, without the same single-interval scale. So the 66-item form derives from the 88-item form and adds the Rasch-based scoring, giving a unified, interval-scale score, while the 88-item form provides more items but with ordinal interpretation.