The HPI serves as a timely, accurate indicator of house price trends at various geographic levels. It also offers a calculator that does not project the actual value of any particular house, but instead what a given house purchased at a point in time would be worth today if it appreciated at the average appreciation rate of all homes in the area.
Very fun tool provided by the Federal Government if you click here
Here is some information about Long Island:
Nassau-Suffolk, NY (MSAD)
1 Quarter -1.36
1 Year -5.80
5 Years 1.30
So while prices are down this year, they are still up over 5 years.