What is the relationship between Janet Yellen and president 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.

The significance of this year's Jackson Hole event has been talked down by some observers due to the absence of US Federal Reserve chair Janet Yellen and European Central Bank president Mario Draghi.

Answer: position_held