I have two values (mean MMSE scores recorded at pre-test and post-test for individuals in an intervention group) with differing standard deviations. I have calculated the absolute mean difference by subtracting the post-test value from the pre-test value. I am now attempting to calculate the standard deviation for the mean difference value. I am unsure of how to do this and would appreciate some clarification. For context, these are continuous outcome measures. I have attached the calculation I have used so far, but I am unsure if this is the correct way of calculating the standard difference.
This should be the same as any other paired comparison t-Test where you use the pooled variance. This option should be easy to locate in your software.
Since you did find differences in the variance at the two times, I recommend creating scatter plot to examine this. The classic format in your case would put Time-1 data on the X axis (horizontal) and the Time-2 data on the Y axis (vertical).
Dear Marya,
If this is your study and you have the raw data, you can calculate standard deviation easily by calculating post-pre means for each participant, and you can even calculate the STDEV in excel.
However, if this is not for your study and if you are looking for a meta-analysis, read my paper and see your options: Article The Effects of Resistance Training on Architecture and Volum...
Regards,
Gokhan
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