Yes, great questions! The SEM can be a bit confusing. Some researchers use the SEM equivalent to the MDC/MDD, but the preferred calculation for the MDC/MDD is MDC (95) = 1.96 × √ 2 × SEM where 1.96 is the z score associated with the 95% confidence level and SEM includes the pooled standard deviation (SD) and the ICC. Therefore, the SEM is included it the calculation, but not the absolute value. Relative to CP, we know that children in GMFCS level III are more variable in their motor performance compared to levels I and II. Therefore, it is not a surprise to see higher SEMs for outcome measures in level III compared to levels I and II.
We hope these responses help in your journey through the weeds!