The average is not as useful a statistic as the median per square foot, because an outlier property on either the high or the low end can seriously skew averages. So take all the numbers with a grain of salt.
In commercial real estate square footage is king, but in the residential world things are a lot more complicated, especially when we're talking a neighborhood full of grand old brownstones.
I know that location well and have sold properties in Park Slope. If this is a walk-up in poor condition, the price per square foot will be considerably lower compared with a property in great condition, with original details, and on a low floor or with an elevator.
Licensed Real Estate Salesperson