Hello,

I'm interested in calculating the variability over time of a variable that can takes either positive or negative values. If they were only positive values, I could calculate the standard deviation and the coefficient of variation but here with both positive and negative values, I'm really confused. I understand that computing a CV is weird. What about the SD?

Which kind of data transformation could I use to deal with this problem and be able to assess the variability of this values over time? (I have 4 positive or negative values every 6 months in a longitudinal study).

Thank you very much for your help,

Cheers
PM