I found this article interesting in that it quantified what I have said before relative to how much of an impact residential investors had on the market. I suggest that you read the article on the site to see all the charts.
The charts reveal some astonishing facts. At the peak of the boom in 2006, over a third of all U.S. home purchase lending was made to people who already owned at least one house. In the four states with the most pronounced housing cycles, the investor share was nearly half—45 percent. Investor shares roughly doubled between 2000 and 2006. While some of these loans went to borrowers with “just” two homes, the increase in percentage terms is largest among those owning three or more properties. In 2006, Arizona, California, Florida, and Nevada investors owning three or more properties were responsible for nearly 20 percent of originations, almost triple their share in 2000.