Sales price vs Assessed Values

This data comes from the assessed town values from The Town of Bourne website and the selling prices of homes comes from our local MLS (multiple listing service). In 6 months in Bourne, MA, from 12/29/08 to 5/29/09, there were 54 properties sold. Just 10 sold over the town assessment. The rest sold under the towns assessment - and, in some cases, significantly under. I know this is not an exact science but we had new town assessments that came out last Fall and they were lowered for most properties (except for waterfront properties it appeared). I thought that current sales prices might be pretty close to the latest town assessments. They weren't. I know it doesn't really 'mean' anything, but since the Buyers are looking at assessed values, and in the interest of keeping my Sellers informed, I thought I would look at the data and I certainly did find it an eye opener.