Question 4: For PASS the SEM was 1.1 and the SRD was 3.2. What do these numbers tell us?
The SEM, standard error of measurement, or within subject standard deviation is the standard deviation of repeated measurements on the same subject. Hence if we were to make repeated observations a few days apart on stroke patients using the PASS, we estimate that their standard deviation would be 1.1.
The SRD, smallest real difference, or repeatability is the upper limit which 95% of differences between pairs of measurements on the same subject would lie below. Hence if a PASS measurement changed by more than 3.2, this is an unusual difference and provides some evidence that the patient has changed.
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Last updated: 22 April , 2008.