Is data visualization worth paying for? In some quarters, this may be a controversial question.
If you are having doubts, just look at some examples of great visualization. This week, the NYT team brings us a wonderful example. The story is about whether dogs feel jealousy. Researchers have dog owners play with (a) a stuffed toy shaped like a dog (b) a Jack-o-lantern and (c) a book; and they measured several behavior that are suggestive of jealousy, such as barking or pushing/touching the owner.
This is how the researchers presented their findings in PLOS:
And this is how the same chart showed up in NYT:
Same data. Same grouped column format. Completely different effect on the readers.
Let's see what the NYT team did to the original, roughly in order of impact:
Added a line above the legend, explaining that the colors represent different experimental conditions
Re-ordered the behavior by their average prevalence from left to right
Added little cartoons to make the chart more fun to look at
Added colors and removed moire patterns (a Tufte pet peeve)
Changed the vertical scale from 0 to 1 (scientific) to 0-100
Reduced the number of tick marks on the vertical scale (this is smart because the researchers observed only about 30 dogs so only very large differences are of practical value)
Clarified certain category details, e.g. Snapping became "bite or snap at object"
Removed technical details of p-values, not important to NYT readers
Even simple charts illustrating simple data can be done well or done poorly.
Note to New York metro readers: I'm an invited speaker at NYU's "Art and Science of Brand Storytelling" summer course which starts tomorrow. I will be speaking on Thursday, 12-1 pm. You can still register here.
The home run data set, compiled by ESPN and visualized by Mode Analytics, is pretty rich. I took a quick look at one aspect of the data. The question I ask is what differences exist among the 10 hitters that are highlighted in the previous visualization. (I am not quite sure how those 10 were picked because they are not the Top 10 home run hitters in the dataset for the current season.)
The following chart focuses on two metrics: the total number of home runs by this point in the season; and the "true" distances of those home runs. I split the data by whether the home run was hit on a home field or an away stadium, on the hunch that we'd need to correct for such differences.
The hitters are sorted by total number of home runs. Because I am using a single season, my chart doesn't suffer from a cohort bias. If you go back to the original visualization, it is clear that some of these hitters are veterans with many seasons of baseball in them while others are newbies. This cohort bias explains the difference in dot densities of those plots.
Having not been following baseball recently, I don't know many of these names on the list. I have to look up Todd Frazier - does he play in a hitter-friendly ballpark? His home to away ratio is massive. Frazier plays for Cincinnati, at the Great American Ballpark. That ballpark has the third highest number of home runs hit of all ballparks this season although up till now, opponents have hit more home runs there than home players. For reference, Troy Tulowitzki's home field is Colorado's Coors Field, which is hitter's paradise. Giancarlo Stanton, who also hits quite a few more home runs at home, plays for Miami at Marlins Park, which is below the median in terms of home run production; thus his achievement is probably the most impressive amongst those three.
Josh Donaldson is the odd man out, as he has hit more away home runs than home runs at home. His O.co Coliseum is middle-of-the-road in terms of home runs.
In terms of how far the home runs travel (bottom part of the chart), there are some interesting tidbits. Brian Dozier's home runs are generally the shortest, regardless of home or away. Yasiel Puig and Giancarlo Stanton generate deep home runs. Adam Jones Josh Donaldson, and Yoenis Cespedes have hit the ball quite a bit deeper away from home. Giancarlo Stanton is one of the few who has hit the home-run ball deeper at his home stadium.
The baseball season is still young, and the sample sizes at the individual hitter's level are small (~15-30 total), thus the observed differences at the home/away level are mostly statistically insignificant.
The prior post on the original graphic can be found here.
Making data graphics interactive should improve the user experience. In practice, interactivity too often becomes overhead, making it harder for users to understand the data on the graph.
Reader Joe D. (via Twitter) admires the statistical sophistication behind this graphic about home runs in Major League Baseball. This graphic does present interesting analyses, as opposed to acting as a container for data.
For example, one can compare the angle and distance of the home runs hit by different players:
One can observe patterns as most of these highlighted players have more home runs on the left side than the right side. However, for this chart to be more telling, additional information should be provided. Knowing whether the hitter is left- or right-handed or a switch hitter would be key to understanding the angles. Also, information about the home ballpark, and indeed differentiating between home and away home runs, are also critical to making sense of this data. (One strange feature of baseball fields is that they all have different dimensions and shapes.)
But back to my point about interactivity. The original chart does not present the data in small multiples. Instead, the user must "interact" with the chart by clicking successively on each player (listed above the graphic).
Given that the graphic only shows one player at a time, the user must use his or her memory to make the comparison between one player and the next.
The chosen visual form discourages readers from making such comparisons, which defeats one of the primary goals of the chart.
Back in 2008, I wrote about this unfortunate chart by the Guardian (link):
The barrel imagery interferes with communicating the data. The green portion looks about the same size as the red portion when the number is four times smaller.
This week, the staff at WSJ publish a similar chart in this article about North Dakota fracking.
They kind of recognize the distortion and utilize a horizontal cutup instead of following the edge of the barrel. But it doesn't really fix the problem if you look at how 3 percent at the top and at the bottom of the barrel are portrayed.
It's not clear to me why they don't use a simple stacked column chart with horizontal text labels.
Alberto links to a nice Propublica chart on average annual spend per dialysis patient on ambulances by state. (link to chart and article)
It's a nice small-multiples setup with two tabs, one showing the states in order of descending spend and the other, alphabetical.
In the article itself, they excerpt the top of the chart containing the states that have suspiciously high per-patient spend.
Several types of comparisons are facilitated: comparison over time within each state, comparison of each state against the national average, comparison of trend across states, and comparison of state to state given the year.
The first comparison is simple as it happens inside each chart component.
The second type of comparison is enabled by the orange line being replicated on every component. (I'd have removed the columns from the first component as it is both redundant and potentially confusing, although I suspect that the designer may need it for technical reasons.)
The third type of comparison is also relatively easy. Just look at the shape of the columns from one component to the next.
The fourth type of comparison is where the challenge lies for any small-multiples construction. This is also a secret of this chart. If you mouse over any year on any component, every component now highlights that particular year's data so that one can easily make state by state comparisons. Like this for 2008:
You see that every chart now shows 2008 on the horizontal axis and the data label is the amount for 2008. The respective columns are given a different color. Of course, if this is the most important comparison, then the dimensions should be switched around so that this particular set of comparisons occurs within a chart component--but obviously, this is a minor comparison so it gets minor billing.
I love to see this type of thoughtfulness! This is an example of using interactivity in a smart way, to enhance the user experience.
The Boston subway charts I featured before also introduce interactivity in a smart way. Make sure you read that post.
Also, I have a few comments about the data analysis on the sister blog.
Announcement: I'm giving a free public lecture on telling and finding stories via data visualization at NYU on 7/15/2014. More information and registration here.
The Economist states the obvious, that the current World Cup is atypically high-scoring (or poorly defended, for anyone who've never been bothered by the goal count). They dubiously dub it the Brazil effect (link).
Perhaps in a sly vote of dissent, the graphic designer came up with this effort:
(Thanks to Arati for the tip.)
The list of problems with this chart is long but let's start with the absence of the host country and the absence of the current tournament, both conspiring against our ability to find an answer to the posed question: did Brazil make them do it?
Turns out that without 2014 on the chart, the only other year in which Brazil hosted a tournament was 1950. But 1950 is not even comparable to the modern era. In 1950, there was no knock-out stage. They had four groups in the group stage but divided into two groups of four, one group of three and one group of two. Then, four teams were selected to play a round-robin final stage. This format is so different from today's format that I find it silly to try to place them on the same chart.
This data simply provide no clue as to whether there is a Brazil effect.
The chosen design is a homework assignment for the fastidious reader. The histogram plots the absolute number of drawn matches. The number of matches played has tripled from 16 to 48 over those years so the absolute counts are highly misleading. It's worse than nothing because the accompanying article wants to make the point that we are seeing fewer draws this World Cup compared to the past. The visual presents exactly the opposite message! (Hint: Trifecta Checkup)
Unless you realize this is a homework assignment. You can take the row of numbers listed below the Cup years and compute the proportion of draws yourself. BYOC (Bring Your Own Calculator). Now, pay attention because you want to use the numbers in parentheses (the number of matches), not the first number (that of teams).
Further, don't get too distracted by the typos: in both 1982 and 1994, there were 24 teams playing, not 16 or 32. The number of matches (52 in each case) is correctly stated.
Wait, the designer provides the proportions at the bottom of the chart, via this device:
I find the legend challenging as well. The presentation should be flipped: look at the proportion of ties within each round, instead of looking at the overall proprotion of ties and then breaking those ties by round.
The so-called "knockout round" has many formats over the years. In early years, there were often two round-robin stages, followed by a smaller knockout round. Presumably the second round-robin stage has been classified as "knockout stage".
Also notice the footnote, stating that third-place games are excluded from the histogram. This is exactly how I would do it too because the third-place match is a dead rubber, in which no rational team would want to play extra-time and penalty shootout.
The trouble is inconsistency. The number of matches shown underneath the chart includes that third-place match so the homework assignment above actually has a further wrinkle: subtract one from the numbers in parentheses. The designer gets caught in this booby trap. The computed proportion of draws displayed at the bottom of the chart includes the third-place match, at odds with the histogram.
Here is a revised version of the chart:
A few observations are in order:
The proportion of ties has been slowly declining over the last few Cups.
The drop in proportion of ties in 2014 is not drastic.
While the proportion of ties has dropped in the 2014 World Cup, the proportion of 0-0 ties has increased. (The gap between the two lines shows the ties with goals.)
In later rounds, since the 1980s, the proportion of ties has been fairly stable, between 20 and 35 percent.
Another reason for separate treatment is that the knockout stage has not started yet in 2014 when this chart was published. Instead of removing all of 2014, as the Economist did, I can include the group stage for 2014 but exclude 2014 from the knockout round analysis.
In the Trifecta Checkup, this is Type DV. The data do not address the question being posed, and the visual conveys the wrong impression.
Finally, there is one glaring gap in all of this. Some time ago (the football fans can fill in the exact timing), FIFA decided to award three points for a win instead of two. This was a deliberate effort to increase the point differential between winning and drawing, supposedly to reduce the chance of ties. Any time-series exploration of the frequency of ties would clearly have to look into this issue.