Football rankings 2
Jan 17, 2008
The above chart is another one in the NYT series on the NFL playoffs. It evaluates the mix of passing and rushing attempts by offense. The convoluted way by which the caption strains to tell a story indicates trouble ahead:
Of the three playoff teams that threw the ball the most, two of them come from cities known for cold weather. Conversely, of the three teams that ran the most, two of them play their home games in milder weather.
The implication is that teams from cold-weather cities are supposed to want to rush more, and vice versa. And the data (total of six samples) pointed to the opposite.
This presentation suffers from low data-to-ink ratio: too much ink is spilled over not much data. The designer arbitrarily picks one of the two variables (passing attempts, rushing attempts) as the primary, sorting variable -- trace the orderly green diamonds on the right chart. This makes it hard to see a pattern in the brown diamonds. As usual, a scatter plot works much better with two data series.
In the junkart version, the raw numbers of attempts are converted into proportion of attempts that were passing versus rushing. This easy move immediately collapses the two dimensions into one. Now, we have room to include an extra variable which matters: the average amount of snowfall in these cities.
So what does the data say about the relationship between propensity to pass and cold weather? There appears to be very little relationship as the dots are all over the chart. In particular, the teams playing in cities with the highest snowfall span the range of passing percents; similarly, those playing in lowest-snowfall cities also span the range of passing percents.
The caption ignores all the blue dots, focusing only on the gray ones. A more direct examination of the relationship reveals the folly of the so-called "not so conventional wisdom".
References: "NFL Offences Undergo a Thaw in Thinking", New York Times, Jan 5 2008; government snowfall statistics.
Passing and rushing are supposed to be a pair of "activities in football" somehow opposed to each other, so instead of a cluster bar graph, I would suggest (surprise!) a tornado graph (back-to-back bar graph). This could be paired with a dot plot of snowfall, and the two graphs sorted in order of snowfall.
If the top three passers and top three rushers were marked in some way with color or asterisks, this graphical table could be directly interrogated to establish whether the text in the caption was a reasonable summary.
Posted by: derek | Jan 18, 2008 at 07:41 AM
Even the Times should have been smart enough not to include an indoor-stadium team like Indy on a chart correlating play calls with weather. The whole idea was dumb to begin with.
Posted by: Dan | Jan 18, 2008 at 05:32 PM
wouldn't it have been better if the original chart was sorted on snowfall levels?
Then it would have looked like the scatter plot but with two dots per team.
Posted by: DaveG | Jan 23, 2008 at 11:54 AM