In many parts of the country house prices are rising faster than rents, making it difficult to find investment opportunities that will cash flow. A new analysis by RealtyTrac takes a closer look at where median home prices and average rental rates make for good — and not so good — returns on rental properties. That rental return, by the way, for each county is the gross rental yield, calculated by taking the 2014 fair market rent for a three-bedroom home multiplied by 12 (months) and then dividing that 12-month total by the median sales price of residential properties in the county. Here's what they found: