# Is there a statistical measure for how much a variable fluctuates over time?

Is there a statistical measure for how much a variable fluctuates over time? For example a noise signal fluctuates a lot. However, if you would sort all values of the signal in time, you would have a signal that does not fluctuate at all. My first idea was to use the variance of the derivative, but I’m not sure whether this is the best measure. Another idea might be to use information entropy, but I’m not sure how to approach it that way.

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rate_of_change = d(variable)/d(time)