Is it worth the drama?

Quite the eye-catching chart this:

Wsj_avianflu

The original accompanied this article in the Wall Street Journal about avian flu outbreaks in the U.S.

The point of the chart appears to be the peak in the flu season around May. The overlapping bubbles were probably used for drama.

A column chart, with appropriate colors, attains much of the drama but retains the ability to read the data.

Redo_avianflu2

 


Tricky boy William

Last week, I was quite bothered by this chart I produced using the Baby Name Voyager tool.

Bnv_william

According to this chart, William has drastically declined in popularity over time. The name was 7 times more popular back in the 1880s compared to the 2010s. And yet, when I hovered over the chart, the rank of William in 2013 was 3. Apparently, William was the 3rd most popular boy name in 2013.

I wrote the nice people at the website and asked if there might be a data quality issue, and their response was:

The data in our Name Voyager tool is correct. While it may be puzzling, there are definitely less Williams in the recent years than there were in the past (1880s). Although the name is still widely popular, there are plenty of other baby names that parents are using. In the past, there were a limited amount of names that parents would choose, therefore more children had the same name.

What bothered me was that the rate has declined drastically while the number of births was increasing. So, I was expecting William to drop in rank as well. But their explanation makes a lot of sense: if there is a much wider spread of names in recent times, the rank could indeed remain top. It was very nice of them to respond.

***

There are three ways to present this data series, as shown below. One can show the raw counts of William babies (orange line). One can show the popularity against total births (what Baby Name Wizard shows, blue line). One can show the rank of William relative to all other male baby names (green line). Consider how different these three lines look!

Jc_william_3metrics

The rate metric (per million births) adjusts for growth in total births. But the blue line is difficult to interpret in the face of the orange line. In the period 1900 to 1950, the actual number of William babies went up but the blue line came down. The rank is also tough especially in the 1970-2000 period when it took a dive, a trend not visible in either the raw counts or the adjusted counts.

Adding to the difficulty is the use of the per-million metric. In the following chart, I show three different scales for popularity: per million, per 100,000, and per 100 (i.e. proportion). The raw count is shown up top.

Jc_william_4scale

All three blue lines are essentially the same but how readers interpret the scales is quite another matter. The per-million births metric is the worst of the lot. The chart shows values in the 20,000-25,000 range in the 1910s but the actual number of William babies was below 20,000 for a number of years. Switching to per-100K helps but in this case, using the standard proportion (the bottom chart) is more natural.

***

The following scatter plot shows the strange relationship between the rate of births and the rank over time for Williams babies.

Jc_william_rank_prop

Up to 1990s, there is an intuitive relationship: as the proportion of Williams among male babies declined, so did the rank of William. Then in the 1990s and beyond, the relationship flipped. The proportion of Williams among male babies continued to drop but the rank of William actually recovered!

 

 


There are no easy charts

Every chart, even if the dataset is small, deserves care. Long-time reader zbicyclist submits the following, which illustrates this point well.

Nhane_obesity

The following comments are by zbicyclist:

This is from http://win.niddk.nih.gov/statistics/  -- from the National Institute of Diabetes and Kidney Diseases, part of the U.S. National Institutes of Health.
 
The pie chart is terrible in a pedestrian way – a bar chart could be so much clearer, or even a table. You have to do too much work to match up the colors, numbers and labels on the pie chart.

To the right of the pie is a bar chart, but a bar chart in which the categories are nested – extreme obesity is part of obesity, extreme obesity and obesity are part of overweight or obesity.  If we want to do something like this, there should be 3 charts (e.g. space on the x axis indicating a break). The normal expectation for a bar graph is that the categories are mutually exclusive.  This problem is repeated in the Race/Ethnicity graph just below these.

***

Now, some comments by me.

Another issue of the design is inconsistency. The same color scheme is used in both charts but to connotate different concepts.

Redo_nhanes_obesity

Put yourself at the moment when you just understood the chart on the left side. You figured out that obesity is deep green while extreme obesity is light green. Now you shifted your attention to the column chart. You were expecting the light green columns to indicate extreme obesity, and the deep green, obesity. And yet, the light/dark green represents a male-female split.

Here is a stacked column chart showing that females are more likely than males to be either extremely obese or not overweight. In other words, the female distribution has "fatter tails".

Redo_nhanes_obesity_2

I learned the most upsetting thing about this chart when re-making it: the listed percentages on the pie chart added up to 106 percent.

 


Losing sleep over schedules

Fan of the blog, John H., made a JunkCharts-style post about a chart that has been picked as a "Best of" for 2014 by Fast Company (link). I agree with him. It seems more fit to be on the "Worst of" list. Here it is:

Sleep-schedules

As John pointed out, the outside yellow arc (Beethoven) and the inside green arc (Simenon) present, shockingly, the same exact sleep schedule (10 pm to 6 am).

John unrolled the arcs and used R to make this version:

JWHendy_sleep-times-early-first

Go here to read John's entire post.

***

Another improvement is to add a "control". One way to understand how unusual these sleep patterns are is to compare them to the average person.

I'm also a little dubious as to the reliability of this data. How do we know their sleep schedules? And how variant were their schedules?

If I rate this via the Trifecta Checkup, I'd classify this as Type DV.

 

 


Relevance, to you or me: a response to Cairo

Alberto Cairo discussed a graphic by the New York Times on the slowing growth of Medicare spending (link).

Medicarespend_combinedThe chart on the top is published, depicting the quite dramatic flattening of the growth in average spending over the last years--average being the total spend divided by the number of Medicare recipients. The other point of the story is that the decline is unexpected, in the literal sense that the Congressional Budget Office planners did not project its magnitude. (The planners did take the projections down over time so they did project the direction correctly.)

Meanwhile, Cairo asked for a chart of total spend, and Kevin Quealy obliged with the chart shown at the bottom. It shows almost straight line growth.

Cairo's point is that the average does not give the full picture, and we should aim to "show all the relevant data".

***

I want to follow that line of thinking further.

My first reaction is Cairo did not say "show all the data", he said "show the relevant data".  That is a crucial difference. For complex social problems like Medicare, and in general, for "Big Data", it is not wise to show all the data. Pick out the data of interest, and focus on those.

A second reaction. How can "relevance" be defined? Doesn't it depend on what the question is? Doesn't it depend on the interests and persuasion of the chart designer (or reader)? One of the key messages I wish to impart in my book Numbersense (link) is that reasonable people using uncontroversial statistical methods to analyze the same dataset can come to different, even opposite, conclusions. 

Statistical analysis is concerned with figuring what is relevant and what isn't. This is no different from Nate Silver's choice of signal versus noise. Noise is not just what is bad but also what is irrelevant.

In practice, you present what is relevant to your story. Someone else will do the same. The particular parts of the data that support each story may be different. The two sides have to engage each other, and debate which story has a greater chance of being close to the truth. If the "truth" can be verified in the future, the debate is more easily settled.

Unfortunately, there is no universal standard of relevance.

***

Going back to the NYT story. The chart on total Medicare spending is not as useful as it may seem. This is because an aggregate metric like this for a social phenomenon is influenced by a multitude of factors. Clearly, population growth is a notable factor here. When they use the word "real", I don't know if this means actualized (as opposed to projected), or "in real terms" (that is, inflation adjusted). If not the latter, the value of money would be another factor affecting our interpretation of the lines.

Without some reference levels for population and value of money, it is hard to interpret whether the straight-line growth implies higher or lower spending intensity. For the second chart, I suggest plotting the growth in the number of Medicare recipients. I believe one of the goals of the Affordable Care Act is to reduce the ranks of the uninsured so a direct depiction of this result is interesting.

The average spend can be thought of as population-adjusted. It is a more interpretable number -- but as Cairo pointed out, it is also narrow in scope. This is a tradeoff inherent in all of statistics. To grow understanding, we narrow the scope; but as we focus, we lose the big picture. So, we compile a set of focal points to paint a fuller picture.

 

 


A small step for interactivity

Alberto links to a nice Propublica chart on average annual spend per dialysis patient on ambulances by state. (link to chart and article)

Propublica_ambulance

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:

Propublica_ambulance_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.


Light entertainment: famous people, sleep, publication bias

Bernard L. tipped us about this "infographic":

3031754-inline-i-sleep-schedule

The chart is missing a title. The arcs present "sleep schedules" for the named people. The "data" comes from a book. I wonder about the accuracy of such data.

Also note the inherent "publication bias". People who do not follow a rigid schedule will not be able to describe a sleep schedule, thus taking themselves out of the chart.


The Numbers Guy went on vacation

Carl Bialik used to be the Numbers Guy at Wall Street Journal - he's now with FiveThirtyEight. Apparently, he left a huge void. John Eppley sent me to this set of charts via Twitter.

This chart about Citibike is very disappointing.

Ss_spincity

Using the Trifecta checkup, I first notice that it addresses a stale question and produces a stale answer. The caption below the chart says "the peak times ... seem to be around 9 am and 6 pm." What a shock!

I sense a degree of meekness in usnig "seem to be". There is not much to inspire confidence in the data: rather than the full statistics which you'd think someone at Citibike has, the chart is based on "a two-day sample last autumn". The number of days is less concerning than the question of whether those two autumn days are representative of the year. Curious readers might want to know what data was collected, how it was collected, and the sample size.

Finally, the graph makes a mess of the data. While the black line appears to be data-rich, it is not. In fact, the blue dots might as well be randomly scattered and connected. As you can see from the annotations below, the scale of the chart makes no sense.

Jc_wsj_citibike

Plus, the execution is sloppy, with a missing data label.

***

 The next chart is not much better.

Wsj_babybumps

The biggest howler is the choice of pie charts to illustrate three numbers that are not that different.

But I have to say the chart raises more questions than it answers. I am not an expert in pregnancy but doesn't a pregnant woman's weight include the weight of the baby she's carrying? So the more weight the woman gains, on average, the heavier is her baby. What a shock!

***

 The last and maybe the least is this chart about basketball players in the playoff.

Wsj_fabfive

It's the dreaded bubble chart. The players are arranged in a perplexing order. I wonder if there is a natural numbering system for basketball positions (center = #1, etc.), like there is in soccer. Even if there is such a natural numbering system, I still question the decision to confound that system with a complicated ranking of current-year playoff players against all-time players.

Above all, the question being asked is uninteresting, and so the chart is uninformative. A more interesting question to me is whether the best players are playing in this year's playoff. To answer this question, the designer should be comparing only currently active players, and showing the all-time ranks of those players who are playing in the playoffs versus those who aren't.

 


Losing the big picture

One of the dangers of "Big Data" is the temptation to get lost in the details. You become so absorbed in the peeling of the onion that you don't realize your tear glands have dried up.

Hans Rosling linked to a visualization of tobacco use around the world from Twitter (link to original). The setup is quite nice for exploration. I'd call this a "tool" rather than a visual.

***

Tobaccouse_1Let's take a look at the concentric circles on the right.

I appreciate the designer's concept -- the typical visualization of this type of data is looking at relative rates, which obscures the fact that China and India have far and away the most smokers even if their rates are middling (24% and 13% respectively).

This circular chart is supposed to show the absolute distribution of smokers across so-called "super-regions" of the world.

Unfortunately, the designer decided to pile on additional details. The concentric circles present a geography lesson, in effect. For example, high-income super-region is composed of high-income North America, Western Europe, high-income Asia Pacific, etc. and then high-income North America is composed of USA, Canada, etc.

Notice something odd? The further out you go, the larger the circular segments but the smaller the amount of people they represent! There are more people in the super-region of high-income worldwide than in high-income North America and in turn, there are more people in the high-income North American region than in USA. But the size of the graphical elements is reversed.

***

Tobaccouse_2In principle, the "bumps"-like chart used to show the evolution of tobacco prevalence in individual countries make for a nice visual. In fact, Rosling marvelled that the global rate of consumption has fallen in recent years.

However, I'm often irritated when the designer pays no attention to what not to show. There are probably well above 200 lines densely packed into this chart. It is almost for sure that over-plotting will cause some of these lines to literally never see the light of day. Try hovering over these lines and see for yourself.

The same chart with say 10 judiciously chosen lines (countries or regions) provides the reader with a lot more profit.

***

The discerning reader figures out that the best visual actually does not even show up on the dashboard. Go ahead, and click on the tab called "Data" on top of the page. You now see a presentation of each country's "data" by age group and by gender. This is where you can really come up with stories for what is going on in different countries.

For example, the British have really done extremly well in reducing tobacco use. Look at how steep the declines are across the board for British men (in most parts of the world, the prevalence of smoking is much higher among men than women.)

Tobaccouse_ukmen

Bulgaria on the other hand shows a rather odd pattern. It is one of the few countries in the bumps chart that showed a climb in smoking rates, at least in the early 2000s. Here the data for men is broken down into age groups.

Tobaccouse_bulgariamen

 
This chart exposes a weakness of the underlying data. The error bars indicate to us that what is being plotted is not actual data but modeled data. The error bars here are enormous. With the average at about 40% to 50% for many age groups, the confidence interval is also 40% wide. Further, note that there were only three or four observations (purple dots) and curves are being fitted to these three or four dots, plus extrapolation outside the window of observation. The end result is that the apparent uplift in smoking in the early 2000s is probably a figment of the modeler's imagination. You'd want to understand if there are changes in methodologies around that time.

As a responsible designer of data graphics, you should focus less on comprehensiveness and focus more on highlighting the good data. I'm a firm believer of "no data is better than bad data".