A wave of ambitious social-network experiments is underway in the U.S. and Europe to track our movements, probe our relationships and, ultimately, affect the individual choices we all make. WSJ's Robert Lee Hotz reports.
A wave of ambitious social-network experiments is underway in the U.S. and Europe to track our movements, probe our relationships and, ultimately, affect the individual choices we all make. WSJ's Robert Lee Hotz reports.