Utilize the input text as a context reference, choose the right relationship between GfK and Market research from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

Market research company GfK (Swiss: GFK.SW - news ) said its monthly sentiment index jumped to +7 in August from +4 in July, matching June's figure, which was the highest since January 2000.

Answer: industry