SIFO is a Swedish company earlier known as Sifo Research International in the area of opinion and social research. The company was founded in 1954 as Svenska institutet för opinionsundersökningar ("the Swedish Institute for Opinion Surveys") and known by the public under the abbreviation SIFO which is one of the strongest brands in Sweden. It is now a subsidiary of TNS Global which is part of the WPP Group plc. SIFO-TNS has its headquarters in Stockholm.
Sifo has since 1967 published its public opinion poll "Voter monitor" (Swedish: Väljarbarometern) which analyses the party allegiances of Swedish voters. Sifo is also known for one of the largest media surveys in the world – ORVESTO Konsument where every year almost 50 thousand people (out of totally 9 million citizens) are interviewed about their media and consumption patterns.
Sifo Research International merged with TNS Gallup during 2009. According to TNS-SIFO's Swedish website the merger is part of a larger reorganisation within the Kantar Group (which in its turn is owned by WPP). The companies Research International, the global brand will be TNS, but local brands such as Research International and SIFO will be used in various countries. In Sweden the brand SIFO is very strong and the official name of the company in Sweden will therefore be TNS-SIFO AB. TNS-SIFO is the largest market research company in Sweden.