The matrix is based on voluntary responses from the companies as well as other sources. Security Magazine, which does not purport data to be a complete list or to reflect changing conditions, revenues and officer staffing levels, asked for responses during November and December 2005. Other sources include: the National Association of Security Companies (NASCO); The Security Letter, edited by Robert McCrie; Ricci Communications and its clients; Lehman Brothers 2005 Security Industry Report; the U.S. Department of Labor; SEIU; and individual company materials and their Web sites. If your firm wants to be listed or update a listing, e-mail the Security Magazine Editor Bill Zalud