What is the relationship between Western Electric and at in the context of the input sentence. Choose an answer from: 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.

Annual reviews date back to the 1930s when a Harvard Business School professor, Elton Mayo, studied behavior at a Western Electric Factory.

Answer: parent_organization