What is the relationship between millions and Chicago 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.

An NBER working paper* published this week by Sumit Agarwal of the National University of Singapore, Souphala Chomsisengphet of the Treasury Department, Neale Mahoney of the University of Chicago and Johannes Stroebel of New York University looks at data from hundreds of millions of credit cards from 2008 to 2014 to work out why the results were so disappointing.

Answer: location_of_formation