The USCIS believes that a NIW applicant could not benefit the U.S. national interest by virtue of engaging in the field or seeking an as yet undiscovered solution to the problematic issue. Your additional evidence should establish that you are a researcher who is recognized as outstanding in your field.
Since the RFE you received is very general, it means that the USCIS will not approve a NIW petition simply because you meet the basic NIW requirements. Therefore, you reply of RFE should always show that:
1) you seek employment in an area of substantial intrinsic merit;
2) your employment should be national in scope;
3) you are recognized as outstanding in your field.
For RFE of NIW replying, please also see: http://www.greencardapply.com/rfe.htm