The Boston Globe reports today that Single Family home sales are down 5 percent in December from a year ago with condominium sales state-wide tanking an even greater dip.  Downtown Boston held the course with sales at year end up 2% over 2010, which was a very good year for sales, dollar volume, average and median selling price.  Lack of Inventory is helping to push values up in Downtown Boston.  Today there are fewer choices for Buyers than there were one year ago according to data from the Multiple Listing Service; MLS/Pin.  By our tracking there are, on average, 226 sales per month in Downtown Boston.  Given the current inventory and absorption there is a less than four month supply of properties for sale, 3.5 months to be exact.  Last year at this time there was a 4.3 month supply, the industry standard for a "balanced" market is 5-6 months of inventory.  What is really dramatic is the paucity of listings in the $0-$499,999 range, the available inventory has dropped by 33% and the absorption rate has gone from 4.3 months of inventory to 2.8 months. One has to wonder if some of the development now underway will be converting from rentals to sales over the next two years.