Dear Mr. Squire
Prof. Finke's slide does not include a source for this information, but in his remarks (about 30 minutes into the webcast), when he says "living within 10 miles of your kids; not a good idea," he notes "this is 20,000 retirees", which would seem to be a reference to the Health and Retirement Study. You may want to follow up directly with Prof. Finke (http://www.depts.ttu.edu/pfp/faculty.php) to find out where, specifically, he found this data point.
Thanks for reading Enterprising Investor.
Best,
Lauren