In 2008, Houston received top ranking on Kiplinger's Personal Finance Best Cities of 2008 list, which ranks cities on their local economy, employment opportunities, reasonable living costs, and quality of life. The city ranked fourth for highest increase in the local technological innovation over the preceding 15 years, according to Forbes magazine. In the same year, the city ranked second on the annual Fortune 500 list of company headquarters, first for Forbes magazine's Best Cities for College Graduates, and first on their list of Best Cities to Buy a Home. In 2010, the city was rated the best city for shopping, according to Forbes.
Try to answer this question if possible (otherwise reply "unanswerable"): When was Houston ranked the best city for shopping?
2010