I'm going to take a stab at this and invite feedback where I might have gone astray with my assumptions or calculations, although I certainly can't figure how that might happen.  :^)

With fundamental analysis of equities (particularly publicly-traded, common stocks) one of the key statistics that is of importance is a P/E ratio.  Within certain industries, there are ranges of P/E ratios that are more acceptable than others.   E.G., A high-tech computer manufacturer may have a P/E ratio of 20 while a coal mining company may have a P/E ratio of 10 and their respective industries will dictate whether this is an acceptable Price to Earnings ratio. 

This simply means that for every $1 of net profit the High-tech company makes, the market values this at $20 in stock price.   Case in point, today Hewlett Packard (HPQ) is trading at 44.75.  The most recent EPS figure for the last 12 months was $2.31.  $44.75/2.31 = 19.37, thus the quoted 19.41 P/E ratio is supported.  If HPQ pulls a rabit out of their hat and boosts income by $.50/share, this would lead to a nearly $10 increase in the Price of the stock (.50 * 19.41 = 9.70).  

The inverse of a P/E ratio is a Capitalization Rate.  A P/E ratio of 20 is equivalent to a cap ratio of 5% (1/20 = .05).   The lower the CAP Rate, the better quality the property, supposedly.  If there is less risk, the investors will still make the investment at a lower yield, because the yield is more reliable and comes with less headache.   

While the basic math indicates that a 10% Cap Rate is significantly better than a 6% Cap Rate, the reality is that Class A properties support lower cap rates and Class B/C properties demand a higher Cap Rate before someone will buy.  The risk commands the higher rate of return.  If you have to collect your rents with a police officer in tow, that's an increased risk and an investor would be wise to get compensated for that risk.  

Thus, it's no more prudent to evaluate investments solely by Cap Rate than it is to evaluate stocks solely by P/E ratios.  Cap Rates and P/E ratios only tell part of the story.   We need to understand the demographics, location, and the building's condition, in addition to it's income history -- then we'll be getting the whole picture. 

Question:  Where can one find the figures for what properties are selling for, regionally?   I know a few sites but wanted to see if there are others that I have missed.