# Standard deviation of relative values

#### Pinga

##### New Member
Hi!

I have 5 datasets each for 20 subjects which I have to plot relative to a baseline. To be more specific:
Dataset 1: Contains mean value of the baseline condition
Dataset 2-5: Contain each mean value of the conditions 2-5

Since this is the way I have to analyze these data, this is not a question, if this way of processing these data is correct or not. Rather, I came upon a problem when calculating the relative value for the standard deviations:

It is clear to me that I divide all the mean values from datasets 2-5 each with the mean value of dataset 1 for each subject to normalize them (-> relative data to be able to compare the five datasets across all 20 subjects). And it is also clear to me, that I get a baseline of value 1 for dataset 1.
But what is not clear to me is how to calculate the according relative standard deviations. Can I simply divide the standard deviation of dataset 2-5 each to the standard deviation of the baseline (= dataset 1) for each subject?
And when yes, the second point which confuses me is that I therefore have a "relative" standard deviation for the baseline condition of 1. Shouldn't it be 0, since the baseline condition is compared to the baseline condition?

Any help would be greatly appreciated!