There is a link in the article - http://www.nber.org/papers/w22635.pdf http://www.nber.org/papers/w22635.pdf Seems like they used a PIK number created by the c

There is a link in the article - http://www.nber.org/papers/w22635.pdf http://www.nber.org/papers/w22635.pdf Seems like they used a PIK number created by the census bureau to track individuals and same address to create parent-child link.