Recently, I learnt about the usefulness of Reliable Change Index (RCI) value in determining the clinical significance in intervention study, especially for studies with small sample size.
However, I still have some confusion about the test that I hope someone can help me answer.
(1) When calculating RCI , I know that information regarding the Standard Deviation and test-retest reliability coeficient( coefficient alpha) from normative samples is needed. What I want to ask is where to find these information (do you just look for a paper using the same scale on a non-clinical sample?), and do the sample characteristics need to exact match your current sample (e.g., if the current sample is university student, the SD and r value must also come from a non clinical university students sample).
(2) I also noticed that articles which calculated the RCI values didn't say which paper they based their SD and r value on for the normative sample, so I also want to ask that is it necessary to cite the paper you took the normative Sd and r value.
(3) Regarding the formula, I noticed that while the difference between subject's pre-post test was divided by the standard error of the difference of the test (Sdiff), the formula for calculating Sdiff is sometimes different. Specifically, some tests suggest that we need the Standard Deviation from a normative sample to calculate Standard error of measurement, while other tests said that we need the SD from pre-treatrement group or control group. What is the reason for this?
Thanks everyone for reading
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