Could you provide further explanation on the confidence interval values on this question:
The most appropriate interpretation of change score results between the assessment 6 and assessment 7 administrations would be which of the following?
a. The child made measurable progress with gross motor skills that exceeded the threshold for test error
b. The child plateaued with gross motor skills, as evidenced by the upper limit confidence interval score
c. The child regressed with gross motor skills, as evidenced by a decrease in his percentile score
d. The child made measurable progress with gross motor skills, although he has not exceeded the threshold for test error
Even though a child’s score may change, when the confidence intervals around the two scores overlap, the change may be due to measurement variability or error as opposed to a true functional change.
For Assessment 6 the patient had a GMFM-66 score of 53.09 (CI 50.68-55.50) and for Assessment 7 the patient had a GMFM-66 score of 55.92 (CI 53.63-58.21). The confidence interval takes into account the possibility for test error and gives a range for what numbers we can be 95% confident in that the patient’s score falls between. Since the patient’s confidence intervals from Assessment 6 and 7 overlap (between the scores of 53.63-55.50) it is possible that the patient’s scores actually did not really change if we consider that there could have been test error that is causing the score to be higher or lower than it really should be. So, yes, the patient had a positive change score of 2.83 (measurable change), but since the confidence intervals overlap the scores did not exceed the threshold for test error. Does this help?