Does anyone know how I could do spatial analysis on the area outside of buffers?

Discussion created by gnatzd on Apr 4, 2011
Here is the problem:

I have created buffers of 50 to 100 miles from medical access points.  I have geocoded some patient data for the US.  I am intersed in performing analysis on the areas outside of my buffers (i.e., how many patients are more than 50 to 100 miles from access points?) What is the population density in these areas.  It seems to me that I want to create a shapefile that shows the US area minus the area inside my buffers, but I can't find an easy way to do this.  Please let me know if you have any ideas. Thanks.