Do you want the "average price per square foot," or do you want to know the "median price per square foot"? I would suggest the latter.
The problem with the average (also called the mean) is that extreme values skew the results. For example, if you have a real estate market where there are a few places that sell for, say, $4000 per square foot, while most places are around $500 a square foot, the average will artificially inflate the value you get as an "average."
The median, on the other hand, is the value where half the data points are above it, and half are below it. Extreme values on either end, if few in number, tend not to lead to a result that is unrepresentative.
New York City is most definitely a real estate market with a few properties that have extreme values.
If you'd like to know how to sell your place for the highest possible price, or what you should expect to pay to buy a new place, please send me an email, I'd be happy to help! I work in Brooklyn, Manhattan, Queens and the Bronx.
Karla Harby VP
Charles Rutenberg Realty