Did they control for other influences on labour mobility such as working couples, children, pets, race/colour and car ownership?
A web search for some sentences in the abstract returns some useful hits for the paper online. Someone else posted (after you had posted) a link to the full paper.
Here's a nice PDF. (http://www.piie.com/publications/wp/wp13-3.pdf)
Did they control for other influences on labour mobility such as working couples, children, pets, race/colour and car ownership?