Out in the Hamptons in the fourth quarter, the market for residential real estate looked a lot like Manhattan’s: Inventory was thin and sales volumes were high. A quarterly report from Douglas Elliman showed a 12.2% decrease listing inventories in the final quarter of 2012 from the same time last year. Meanwhile, the median sales price jumped by 16.3% to $907,000. Jonathan Miller, who prepares the Elliman report each year, said it was the lowest inventory figure since he first began tracking it in 2006. Mr. Miller said part of the reason for such low inventory is that many sellers cannot yet afford to trade up. “It’s consistent with a national problem,” Mr. Miller said. “Sellers can’t sell, because they can’t purchase.” The number of Hamptons sales in the last three months of the year was 30.3% higher than during the same period in 2011 at 529. Mr. Miller said the plausible reason for this was that those who were previously unsure decided to go ahead and sell their homes in 2012, ahead of the increased taxes that kicked in at the beginning of this year. “People who were on the fence and who tended to be on the upper end of the market, took action,” Mr. Miller said. Bearing that out, there were seven sales of more than $20 million in the quarter, Mr. Miller said. This skewed the average sales price upward to more than $2.1 million, 34.7% higher than a year prior. Mr. Miller also tracked 49 sales of $5 million and higher, the largest number of such sales he’s seen since he started tracking in 2006. Because of increased sales and low inventories, the absorption rate has dropped. That rate measures the number of months it would take to sell out all inventory at the current sales pace. For the end of 2012, that rate was 5.8 months, down from 8.6 months a year before. Mr. Miller said it is possible that some of the “excess sales” of the end of 2012 will detract from the number of sales in the next few months.