Rhode Island’s real-estate market in January continued to deteriorate, as house prices recorded their steepest month-over-month decline in 19 years, according to a report released yesterday by The Warren Group.

The median price of a single-family house in Rhode Island fell 12.8 percent compared with the previous January — nearly three times the rate in Massachusetts — to $235,000. That marks the largest monthly decline in Rhode Island house prices since the Boston-based research firm began tracking the market in 1989.

The median condo price in Rhode Island fell 13 percent, to $206,500, compared with $237,500 a year earlier, the report said.

Until now, the price declines could be blamed partly on the large number of properties being repurchased by banks at foreclosure auctions. Typically, banks repossess properties to cover the outstanding balances on loans, which may be substantially less than the market value.

The Warren Group’s latest report, however, attempts to more accurately measure the market by excluding from its calculations all properties that banks repurchased at foreclosure auctions, sales between family members and other “non-arm’s length” sales because they tend to distort the statistics, said the research group’s data analyst, Alan Pasnik.

Rhode Island’s prices fell far more sharply than in Massachusetts, where the median price of a single-family house in January dipped 4.4 percent, to $325,000, The Warren Group reported. The median condo price in Massachusetts during the same period ticked down 1.5 percent, to $270,000.

“In a small state like Rhode Island, month-by-month numbers do not always indicate trends,” the company’s chief executive, Timothy Warren Jr., said in a statement. “But we have seen declines in single-family home sales hover around 20 percent for the past five months, and monthly price drops leading up to January have been pushing toward 10 percent.”

Rhode Island’s single-family house sales in January fell 24.3 percent, to 393, compared with 519 sales in January of last year. Condo sales during the same period declined 26.2 percent, to 127, compared with 172 sales a year earlier, the report said.

The Warren Group reported single-family house price declines in Providence, Kent and Washington Counties.

Newport and Bristol Counties reported that prices rose 7.2 percent and 25.5 percent, respectively. (The data do not include Barrington, because the town assessor’s office does not differentiate between types of residential properties or residential and commercial sales.) The median condo price fell in every county except for Bristol, where the median rose about 1.4 percent, The Warren Group reported.