I have a continuous variable (say, sales volume) that I measure for multiple firms over a time period of ten years (but I do not have data across the full ten years for all firms, some drop out, some enter my sample). I want to show that, for each of these firms, there is not a lot of variation in this continuous variable over time, within any given firm.
Added complication: The continuous variable is logged, so it does not have an intuitive interpretation.
What is the best way to show that there is "not much variation," ideally in a single number?
(And yes, I know that there is no technically "correct" answer to this, and "not much variation" is utterly unspecific; I am really just looking for ways to give a reader a quick intuitive sense of whether there is a lot it not a lot of variation over time)