how to code environmental uncertainty

Hi all,

I would like to ask you about how to code "environmental uncertainty" in management study.
My definition of environmental uncertainty is: The standard deviation of the five-year average sales growth across firms in a given industry.
I can understand the definition but it is very challenging to code.
I am using Compustat dataset and data look like below:

firm_id...year... sales.....sic_code
1000.....1999...617.618....3576
1000.....2000...738.921....3576
1000.....2001...843.122....3576
1111.....1995...8921.11....3576
1111.....1996...7121.57....3576
... ...
2000.....1997...1089.23....6324
2000.....1998...1792.21....6324
2000.....1999...1263.18....6324
... ...

I appreciate yout code and comments on this issue!
Regards,