Among the comments about yesterday’s disappointing S&P/Case-Shiller Home Price release were remarks that the data is old or out of date. The report of falling home prices came on the heels of better economic news and some upbeat reports about homebuilders seeing strong orders. Some commentators felt that the news of weaker prices was old news. (see comments at Calculated Risk) While everyone wants up to the minute reports and instant news, there is a trade-off between speed on one side and accuracy and reliability on the other. The infrastructure for buying a house — real estate brokers, mortgages, title insurance, lawyers, recording deeds etc. — is largely a paper-based system involving numerous parts and many different people and steps. Sometimes buying a house seems to mean stepping back into the early 20th century if not the 19th century. As a result, you can’t get data quickly and if you want an accurate picture of what is happening, it takes time. So, unlike stock prices which are available in real time, house prices come with a lag. Further, house prices tend to bounce around a lot, so the indices are reported as three month moving averages to give a better indication of trends. One comment suggested that a weighted average should be used with more weight on the most recent month. This is also a trade-off: putting more weight on one of the three months means more volatility. For the S&P/Case-Shiller indices, the trade-off between speed and accuracy means waiting a little while in exchange for better accuracy.