请问什么是AC尼尔森调查?

http://www.acnielsen.com.cn/company_info.asp
http://www2.acnielsen.com/company/index.shtml

ACNielsen is a U.S. marketing research firm, based in Schaumburg, Illinois. The company serves the consumer goods market with research on market performance and dynamics, solving marketing and sales problems, and identifying market growth opportunities.