Wednesday, June 6, 2007

WSJ Housing Inventory Trends

Check out this Wall Street Journal Interactive graphic showing changes in housing inventory in the past two years. It has some useful and novel features that make exploring the 18 different cities and 3 different regions easier over the past 20 months.

Here's one of the more interesting charts that I created in just a few minutes of exploration.

For the six cities shown (Miami, Orlando, Chicago, Las Vegas, Los Angeles and Phoenix) the upward trends since October 2005 are plain to see.

Try it out yourself and see what you can discover.

Here are my thoughts on the pluses and minuses of these interactive chart features

On the plus side

1. A single click selects a new factor to add to the mix of factors already selected for the chart

2. When adding a new factor into the mix, it highlights that new factor on the chart and reduces the intensity of the other factors on the chart until you move the mouse over the chart again when all factors selected come into full view. This helps you lock in on the colors for the new factor before they become blended with the other factors.

3. When you move the mouse over the check box for a factor that has already been selected, that factor is highlighted against the other factors currently selected with a little pop up text box that tells you the current inventory value exactly.

4. A single click as all that's required to de-select a factor.

5. A single click for one of the three areas (East, Central, West) selects all the factors for that area. And once a whole area has been selected, a single click de-selects all factors currently checked.

6. All of the above pluses add to ease of use and time saving when exploring this data set for the most interesting and telling patterns.

On the minus side

A. Way too short a time range. To make full sense of these trends and put the recent behavior in perspective needs at least 5 years and preferably 10 to 25 years of history.

B. Some major cities that are in the top 10 in population are missing - New York, Philadelphia, and San Antonio.

C. No way to adjust Y axis scaling. This is a serious drawback. The scale runs from zero to 110 thousand which is fine for viewing the trend for Los Angeles which has a range between 45, 000 and 103,000, but it makes it difficult to grasp the trends for such cities as Minneapolis which varies from 25,000 to 31,000 or Baltimore which ranges from 5,000 to 10,000. Both of these cities look flat line during this period even though when you examine them closely they really aren't. Y axis scaling options such as the possibility of calculating the Min-Max scaling for the factors charted would help bring the trends for all cities into clear view.

D. No available view of the data using percentage change from a baseline value for determining the Y axis value. Such a normalizing option would simplify comparisons between cities.

E. No option for showing aggregate results for a region or for stacking the factors selected.

F. If you wish to look at each factor separately, it takes two clicks. One to de-select the previous factor, and one to select the new factor.

G. No option for smoothing with features such as moving averages

H. Missing trend data for other related factors for each city such as
  • Inventory breakdown by New and Existing housing
  • Average number of months houses have been on the market (total, new, existing)
  • Median selling price in that market (total, new, existing)
  • Rate of sales per month in that market (total, new, existing)
  • Number of months of inventory at current sales rate (total, new, existing)
I. Missing option for downloading the underlying data set thereby enabling further analysis.

Hat tip to Barry Ritholtz at The Big Picture

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