"National Intelligence Estimates (NIEs) are often of considerable interest to many Members of Congress. They represent the most formal assessment of a given issue by the U.S. Intelligence Community and address issues of major national security importance which may require congressional action. The intelligence process, however, is not an exact science and, on occasion, NIEs have proved unreliable because they were based on insufficient evidence or contained faulty analysis. This was demonstrated in the NIE produced in 2002 on Iraqi Weapons of Mass Destruction, parts of which were significantly inaccurate. NIEs can provide insights into the likely effects of certain policy approaches, but they are not usually made to take into account the details of planned U.S. diplomatic, economic, military, or legislative initiatives. In the past, Congress was not a principal consumer of NIEs but now appears increasingly interested in obtaining NIEs on crucial security issues despite or perhaps because of the experience with the 2002 Iraq NIE. […]. Some observers assert, however, that public discussion on specific NIEs may not adequately reflect the process by which they are prepared or their inherent limitations. This report will be updated when new information becomes available."
CRS Report for Congress, RL33733