There are plenty of well-understood risk factors for homelessness; addiction, mental illness, poverty. 

But it turns out that even in places where the poverty rates are some of the highest in the nation, homelessness doesn't necessarily follow. One of the biggest risk factors for homelessness is actually pretty simple: it's the cost of housing.

Academic Gregg Colburn and data journalist Clayton Aldern are the authors of the new book Homelessness is a Housing Problem. They join KIRO Newsradio's Dave Ross to talk about their research on rent spikes and real estate bidding wars in cities like Seattle and San Francisco, where tents are on the sidewalks in front of million-dollar homes.