A sign of a mild increase in the strength of the Boston housing market: The average price of homes for sale increased slightly between February and March, according to new data from analytics firm Altos Research. Average list prices in Boston rose 0.5 percent over the previous month, while list prices fell an average of 1.3 percent in a composite of 10 large cities including Boston.

Altos also found a surge in the number of listed properties -- as always happens in the spring -- and a commensurate drop in the age of the average listing.

We talk a lot about all the different ways of measuring the health of a real estate market. The Altos data, which relies on listing prices, is released first, only days after the end of the month. But it also provides the least accurate information. A listing price is just a seller's dream. They may never find a buyer who agrees.

Another few weeks will pass before Warren Group and the Massachusetts Association of Realtors release data on home sales in March. As some of you have noted, that's also an imperfect picture of actual values, because most homes aren't being sold right now.

A few more weeks, and we'll have the Case-Shiller numbers, which try to address that issue, but can't do so completely. And then we'll have the attempts to measure the value of all homes, such as Zillow's new index -- good idea, but the methodology remains controversial.

At any rate, here's the data: Altos says the average listing price in the Boston area in March was $456,958, up from $454,843 in February.