January home prices in the Seattle-Tacoma area fell year-over-year for the first time in an index that tracks values in 20 U.S. metro areas.

Prices fell by 1.3 percent, a far smaller drop than many other areas. The biggest declines were in Las Vegas and Miami, which last month saw drops of 19.3 percent compared to the same month in 2007, according to the S&P/Case-Shiller Home Price Index.

Nationally, prices were down 10.7 percent.

A closely followed means of measuring prices, this index stands out from others for showing the ups and downs over several years. The index ties today's values to where prices stood in January 2000, which gives the Seattle-Tacoma area an index level of 181.6, or home-price growth in the last eight years of 81 percent. That compares to 27.1 percent in Atlanta and 125.4 percent in Miami. (The index looks only at houses and excludes condos.)

Perhaps of concern locally, however, is the months-long trend of smaller and smaller gains and now a decrease in prices. (Northwest MLS numbers show year-over-year price declines in Pierce County five of the last six months.)

Here's a look at the S&P/Case-Shiller year-over-year changes in the last several months for Seattle-Tacoma prices:

January: - 1.3 percent
December: 0.5 percent
November: 1.8 percent
October: 3.3 percent
September: 4.7 percent
August: 5.7 percent
July: 6.9 percent