I received an e-mail from a concerned reader regarding the Canadian Real Estate Association's most recent claim that sales volumes are up across Canada, led by BC and Ontario. Alarm bells went off immediately when I read BC as we already know that Victoria's sales volume number for August is a 20-year-low. How could that mean that sales were up from July when sales were actually down almost 20% month-over-month?
Are sales booming in other parts of the province? No.
How could this possibly be reported as a positive statistic?
Enter seasonally adjusted data, defined as:
Is real estate a seasonal business? We know that Victoria has a pronounced spring buying and selling season as represented by decades of sales statistics. You could make the argument that there is seasonality to the business, much like tourism, because there are months that are traditionally more busy than others.
We also know that when you compare data from say, August 2009 (the month) and August 2010, you're dealing with data from the same month and effectively the same season. Do you need to seasonally adjust the data? No. How about July 2009 with July 2010? No. July 2010 with August 2010? If you believe the summer begins or ends in August, maybe. But really, no.
So why would the CREA and BCREA report sales statistics this way? Because it puts a positive spin on a very poorly performing real estate market.
Different months out-perform other months. You can compare one month to the next, one month of a given year to the same month in previous years and sub-sections of data (e.g. April, May and June) from one year to another. I'm not a statistician or a math whiz by any stretch of the imagination but from a cursory glance I just can't see why you'd want to or need to seasonally adjust real estate sales volumes/dollar-amounts unless you are purposely trying to employ a statistical trick to make data appear favourable.
I know there are several regular commentators here that know far more about stats than I, so I'll ask them to weigh in on this issue in the comments.