Nat Torkington at O’Reilly Radar feels that the New York Times is deliberately distorting the housing market bubble by representing the cost of homes as a line graph in this info-graphic. Nat, and many of the people who have posted comments in response to Nat’s observation, apparently do not understand the difference between line graphs and bar graphs. Nat complains the graphic is misleading because it tries to help the viewer contextualize the information by labeling the starting point, the price of a home in 1987, as “100” so that the viewer would be able to immediately grasp that a $100k house then would worth $160k today. (The graph is adjusted for inflation, so the line represents change relative to inflation.) Instead, the graph could have labeled “100” as “+0” and adjusted the other vertical labels accordingly (“160” becomes “+60%”, etc.) so as not to confuse Nat. Then the graph would have looked like a stock price comparison graph.
Speaking of stock market price graphs, have you ever noticed that they are always presented as line graphs and never go down to 0? That’s because line graphs aren’t intended to show absolute value—that’s the responsibility of bar graphs. Instead, line graphs are used to show the direct relationship between one quantity and another and are often used to represent change over time.
In the case of stock price graphs, the graph shows the relationship of a stock price relative to its starting price over time. In the case of the New York Times info-graphic, the line graph shows the relationship of home price relative to inflation (inflation being the “100” line) over time.
For a line graph, space above the maximum value or below the minimum value (which is what Nat is advocating) is wasted and can be misleading because the added space distorts the relative change that is occurring by flattening the line. Consequently, I find nothing wrong with the New York Times graphic and I believe that Nat’s ideas to improve the graph would only harm it.
If there is an argument to be made about the graph being designed to over-emphasize the bubble, it would the vertical orientation of the map, since line graphs are traditionally wider than they are tall. The placement of text above the peak on the right of the graph also contributes to an exaggerated perception of growth since January, 2000.
