To qualify for the survey, each company is required to submit to third party verification of calendar year revenue for research activities only. Clearly some Top 50 firms have larger revenues if non-research activities are added in. The smallest Top 50 firm in 2000 achieved revenues of US$13.8 million, whilst the largest ACNielsen generated revenues of US$1.6 billion from research operations in more than 100 countries.

ACNielsen Corp., IMS Health Inc. and Information Resources Inc. remain in the top three positions. First ranked ACNielsen Corp achieved 2000 revenues of US$1.6 billion, up 2.1% over 1999. IMS Health Inc. research-only revenues in 2000 stood at US$1.13 billion, up 9.1% from 1999. Information Resources Inc. generated 2000 revenues of US$532 million, down 2.8% from 1999. VNU Inc, newly listed as number four after acquiring Nielsen Media Research, registered research-only revenues (for Nielsen Media Research and NetRatings Inc.) of US$527 million in 2000. Clearly with its acquisition of ACNielsen in early 2001, VNU now ranks as the world’s largest research organisation.

NFO WorldGroup was bumped to number five this year from fourth place on the 2000 list, achieving revenues of US$470 million. Jupiter Media Metrix Inc. has moved up from 34th last year to 18th this year, showing revenues of US$69 million. Harris Interactive also rose on the list from 24th last year to 19th this year, with revenues of US$56 million. Burke Inc. dropped from 19th in 2000 to the 23rd position on this year's list, with revenues of US$48.6 million. The Ziment Group rose from 41st last year to 36th on the 2001 list, with an increase in revenues of more than 30% to nearly US$21 million.

During 2000 the Top 50 firms that made acquisitions were as follows:

• Media Metrix acquired Jupiter Communications in the US and becomes Jupiter Media Metrix,
  
• Total Research acquired Romtec in the UK,
  
• Opinion Research acquired C/J Research in the US,
  
• Maritz Marketing Research acquired Basis-Kontakt in Germany,
  
• Roper Starch Worldwide acquired Parker Tanner in the UK and Langer Associates in the US.