Real estate analysts usually study median prices more closely than the average because of the range of sale prices within the same market.

The median is viewed as a more conservative number that tends to reflect more accurately, in a sample of wide-ranging home prices, what the usual buyer paid.

The average number is the sum of all pieces of data divided by the number of pieces.

It works well for commodity-type products and can help illustrate, for example, what shoppers can expect to pay for socks at a certain store.

The median is the halfway point between the largest and smallest numbers. In housing, that means half of the homes sampled sold for more, half sold for less. Real estate experts use it because it cannot be skewed as easily by sales at the extreme high and low ends of the market.

Consider this set of imaginary transactions: a $150,000 condominium in West Ashley, a $200,000 home on a large lot in Berkeley County, a $250,000 three-bedroom home in Summerville, a $400,000 golf course home in Mount Pleasant and a $1.4 million beach home on the Isle of Palms.

The median price for the sample of homes is $250,000, but the average price is $480,000, a higher price than all but one of the numbers.

For more than 18 months, the market has shown signs of weakness. And basic economics suggests that after a significant drop-off in sales, prices quickly would follow, especially in a market where more than 10,000 sellers are courting an increasingly limited pool of buyers.

But that's not the case, at least not across the entire market.

So far this year, the median sales price for the Charleston region actually has risen by nearly 2 percent to $210,000, while home sales tracked by the local real estate industry's main trade group are off 20 percent through September compared with the same period of 2006.

To a limited degree, sellers have been cutting prices on existing homes in nearly all of the 36 zones where the Charleston Trident Association of Realtors follows sales through its Multiple Listing Service database.

But in a few places, including a section of West Ashley, the level of discounting has reached the point where the median prices for those specific areas has fallen, according to MLS data. Among the reasons: Sellers of existing homes are being forced to compete with deep discounts and incentives offered in brand-new nearby developments.

Sticky notes

The two trends, slumping sales and rising prices, don't seem to make sense. But academic experts say real estate values do not strictly follow the rules of supply and demand. Part of the disconnect stems from what economists call "sticky prices."

The sticky-prices effect occurs when the value of certain services or commodities does not fall significantly even as demand for those services or commodities does, said Frank Hefner, an economics professor at the College of Charleston.

For example, gasoline prices are slow to fall at the pump even when the price of a barrel of oil drops substantially. And the same thing happens in the labor market when work becomes scarce.

"In a boom time, if wages go up from $30,000 to $43,000, they don't cut the wages back down to $30,000 when the recession hits," Hefner said. "They lay you off."

Home prices are unique because a massive pool of individual sellers and buyers, not industry executives, controls the movement of prices, he said.

In the past, sellers who could wait out a downturn for a few years eventually got their asking price, he said.

Some have speculated that the top end of the luxury market has inflated the median home price for Charleston, but it would require a significant increase in the number of sales of those properties to skew the figure. MLS research shows that demand for seven-figure historic homes downtown and vacation homes on the barrier islands has slowed along with the broader market. Even so, prices for luxury properties remain strong.

'In denial'

The resistance among sellers to lower prices is not exclusive to Charleston, said economist Patrick McPherron of Moody's Economy.com, an international economic analysis firm based in West Chester, Pa. Rather, it's a nationwide tendency that's causing the median price either to remain stable or slightly drop in many local and regional housing markets, he said.

Summing up the mentality of many sellers, McPherron said much of "the country's in denial" because sales volume does not support what they are expecting for their homes.

But prices have slipped to a measurable degree in some pockets of Charleston.

Compared with last year, existing homes are selling for less in parts of West Ashley, Johns Island, the Jedburg area and on Daniel Island, according to MLS data.

A similar scenario is playing out on the outskirts of Mount Pleasant, where homes are selling at about the same median price, $404,577, as last year, according to the most recent sales data. There, sellers of existing residences are competing with heavy incentives offered by builders in big developments such as Park West, agents believe.

But the opposite has happened in the other, older half of Mount Pleasant, the section closer to Interstate 526, the Ravenel Bridge and the peninsula. While sales volume has fallen off within the area south of S.C. Highway 41, the median home price has risen steadily, up 18 percent from last year to $369,000.

The pricing power south of Highway 41 can be attributed partly to the town's demographics. Because it's an area where older, more established families live, more sellers are able to handle a second mortgage and avoid offering deep discounts. But he doesn't expect the area's double-digit appreciation rate to carry on for much longer as the competition gets tougher among serious sellers.

Subprime fallout?

Unlike past housing downturns, the current slump features a wild card that could hurt prices in the months ahead: the subprime mortgage crisis.

Subprime refers to a type of loan made during the housing boom to people with checkered credit histories. The concern now is that many of those borrowers will not be able to make their payments once the introductory interest rates on their mortgages rise, forcing banks and other lenders to foreclose on the properties.

Karl Case, an economics professor at Wellesley College in Massachusetts, said rising home foreclosure rates could lead to more housing auctions. And a sell-off of homes on the steps of the county courthouse could dramatically lower home prices across a broad area, he said.

But no one can say with any accuracy how severely the subprime mortgage debt could weigh on the market. It's uncharted financial waters, Case said.

"You really have not tested this subprime stuff before," he said.