# Subjects with different order of magnitude values in panel data

I have quarterly sales data for a variety of stores and would like to estimate the effect of a regulation on sales. A panel type model would appear to be appropriate in this case, with the regulation as a dummy variable.

However, the quantity of sales varies by two-orders of magnitude between stores. How should I account for this?

Apologies for any problems with the question, I am something of a beginner.

• using logs sometimes helps. Log-log models are popular in econometrics, because they are easy to interpret, that is another bonus of using them. – mpiktas Feb 23 '11 at 8:23

• Given that a small minority of my sales data is in the range 0.0 to 1.0, should I add 1 to all my sales figures before using a log transformation? – fmark Mar 6 '11 at 1:02