Rephrase "growth/decrease rate"

I'd like to rephrase the following sentence (Intended to be used in an introduction passage of a paper, regarding a construct from chaos theory, the Maximal Lyapunov exponent)

The Maximal Lyapunov Exponent characterizes a system's average local growth/decrease rate of uncertainty.

In particular, I don't like the "growth/decrease" part. Is there any way to condense it into one word? ("change" doesn't seem appropriate) or else rephrase the whole sentence?

I wasn't sure what tags to use, feel free to add anything that seems appropriate.

Solution 1:

You ask, "Is there any way to condense it into one word? ("change" doesn't seem appropriate) or else rephrase the whole sentence?"

I would take the latter approach. You might try something like:

The Maximal Lyapunov Exponent characterizes the average rate at which a system's local uncertainty either grows or decreases over time.

This captures the idea that the rate is not merely variable, though if you need to be more clear about that idea, it might be better presented in a second sentence.

Solution 2:

How about "decay" instead of decrease? Or maybe reduction in place of decrease. Fluctuation could be used in place of both.