Mystery whiskers: deciphering box plots

Last week was the first Animal Behavior Society virtual meeting. I watched a lot of presentations (which I wrote about over at NeuroDojo: Day 1, Day 2, Day 3, Day 4).

A lot of presentations showed data in box plots, like this:

I’m having a hard time understanding this graph.

This plot shows both the box plot and what I assume is raw data overlaid on top. But the raw data are so scattered in the horizontal, it’s hard to figure out which data points are supposed to be associated with which boxes.

But putting that aside, I’m wondering what people think the plot shows. Because none of the components are labelled.

Here’s another example.

Nothing labelled here, either.

In looking at posters over the years, I have noted that one of the most common problems is that people show something like a bar graph of averages, and show error bars, but nowhere on the poster does it say what the error bars show. Even when I ask, presenters often turn back to the graph to look at it and make a face while trying to remember. They often can’t remember.

The whole advantage of box plots is supposed to be that they provide a more detailed view of the data than a simple average. But you don’t tell me what any of the components in the plot are, then there is no advantage.

That I kept seeing box plots with no description, nothing, made me curious: what do people think are being shown by those whiskers?  (I asked on Twitter, too; most replies here.) Obviously, the person making the graph thought it must be clear. They probably think there is an “industry standard” for box plots, but there is not.

And you can’t just assume that everyone draws box plots the same way you do! Wikipedia notes:

(W)hiskers can represent several possible alternative values, among them:

• The minimum and maximum of all of the data
• One standard deviation above and below the mean of the data
• The 9th percentile and the 91st percentile
• The 2nd percentile and the 98th percentile.

Any data not included between the whiskers should be plotted as an outlier with a dot, small circle, or star, but occasionally this is not done.

Some box plots include an additional character to represent the mean of the data.

On some box plots a crosshatch is placed on each whisker, before the end of the whisker.

Rarely, box plots can be presented with no whiskers at all.

I suspect this is another case of computers making it too easy to draw the wrong thing, as Dan Roam says. People just use the default box plot their graphic software creates and don’t critically examine the output.

I’m just surprised it’s a problem for box plots, since I would maybe expect that if you’re interested enough in showing variation in the data, you’d think about what people need to interpret the variation.

I am not sure what the best solution here is, There are several.

1. Ask if you can replace the box plot with a bar graph, and put “SD” or “SE” or whatever in the Y axis label. Bar graphs cop way too much abuse. (Remember, the context is posters here, not journal articles.)
2. Put the description in fine print under the graph. This is the simplest to achieve.
   
3. Make a legend for the plot. (Origin 2020 does this automatically, so this can be fairly easy in some cases.)
4. Label the elements on the graph the first time you show a box plot. This may be the most clear for a viewer, but is probably the most work for the presenter.

The last two options both have the advantage of putting information at the point of need, on the graph itself.

Link round-up for July 2020

The Journal of Biogeography has an article from its editors about how to make a great figure. heir take-home messages:

1. Create introductory figures to set up your problem.
2. Create figures at final size.
3. Use vector graphics. (Emphatic agreement here!)
4. Make figure captions understandable on their own.
5. Don’t overuse colour.
6. Use maps to show geography.
7. Include node support in phylogenies.
   

There are no figures in this article (!), although it links out to several other articles for figures.

• • • • •

This is a good blog post on choosing colours. In particular, it considers the problem where you are give a style guide and told, “You must use these particular colours, because that’s our brand.”

At one organization I worked for, before I created a data visualization style guide, the guidance for charts was to “use brand green.” This meant that all charts were green, no matter what data they represented. It was hard for readers to tell the difference between graphs in a report, because they all looked the same. Green. To show the complexity of the data, we needed more colors.

Your institution’s colours were probably picked by how they’d look on a t-shirt and not how visible they will look on a graph.

• • • • •

This is a good post on how to make graphs more understandable. Excerpt (which was highlighted as “Important!” in the original):

If you’re going to show people a cumulative graph, it’s important that you tell them it’s a cumulative graph.

• • • • •

Defaults are risky. At least this article on typefaces for research manuscripts suggests so. Because a lot of people do not like Calibri.

• • • • •

A history of emojis from 1862 (!) to today. Some fun tidbits in there, like the role of AOL (remember them?) has by introducing buddy icons in the messenger app.

• • • • •

How did Georgia hide a huge increase in COVID-19 cases?

Map on the left is 2 July 2020. Map on the right is 17 July 2020. Check the legend carefully.

That said,  Jonathan Schwabish offers a counterpoint here. Excerpt:

I believe that the issue of the changing legend is likely due to how the data visualization tool (whatever it is) automatically sets the map bins based on the data.

This is a Hanlon’s razor argument. I used to invoke Hanlon’s razor much more often, but living through 2020 has all but blunted that razor for me. I’ve seen far more heartlessness than cluelessness this year.

• • • • •

This post on the billboard poster format proposed by Mike Morrison is from last September. Excerpt:

I had the most “traffic” at my poster than ever, especially from a more generalized audience. In the past, most of the people who have visited my posters were specialists who picked out keywords from my poster title and were working with the same organism. With the main takeaway of the poster front and center, I also met people who were interested in my methods and intermediate findings and the applications/implications for broader research.

Sorry I missed it then! 

#PlantBio20 is this week!

A quick reminder that I will be speaking at Plant Biology 20 this Wednesday, 29 July!

Wednesday, July 29, 2020, 1:30 PM – 2:30 PM EDT

Get Your Message Across: A Guide to Artwork and Illustrations for Better Impact and Clarity

Speaker:  Magdalena M. Julkowska, PhD – KAUST
Speaker:  Patrice A. Salomé – UCLA
Speaker:  Zen Faulkes
Chair:  Ivan Baxter, Ph.D – Donald Danforth Plant Science Center
Chair:  Mary Williams

One simple trick to improve (some) bar graphs

I ran across this figure because it was being used as a good example.

This is a journal figure, not a poster figure, so there are many things I would want to do differently on a poster. But I just want to focus on one thing:

The most important things to read on this figure are the labels on the x-axis. You’re probably crooking your neck right now trying to do so. Readers should not have to contort themselves to read your graph.

For that matter, the all the y-axis labels also require you crook your neck read them. Even the numbers, which have no business having their being vertically aligned.

But luckily, the solution is simple: rotate it!

Suddenly, this graph becomes easy to scan. No information is lost. The data is not harder to compare. And by definition, the graph takes up the same amount of space on the page. Some tweaking might be required to optimize to columns widths, though.

There are a couple more changes besides rotating the entire image. The old y-axis scales are on the top with a simple rotation, and those got moved to the bottom. The legend and the comparison letters, which were the only things oriented horizontally, got “unrotated” back to horizontal.

If your labels are too wide to be horizontally aligned, consider turning your vertical column graph into a horizontal bar graph.

You don’t want to do this in every case. If you are plotting time as a variable, it is almost always better to keep time on the x-axis, because that is such a standard way of portraying time in graphs. Fortunately, you can often use abbreviations for time (“Jan” or even “J” instead of “January”) to avoid vertical text.

I can’t help you with those taxonomic names, though.

And the moral of the story is: English text wants to be horizontal!

Reference

Seppey CVW et al. 2020. Soil protist diversity in the Swiss western Alps is better
predicted by topo‐climatic than by edaphic variables. Journal of Biogeography 47:866–878. https://doi.org/10.1111/jbi.13755

Review: DesignCap

Having reviewed a couple of online graphic editors this month, I got an email from a company, DesignCap, asking me to do a third. I created an account and logged in.

Wow, it’s a lot like Canva (reviewed last week, here). The user interface, the templates... these two services are clearly trying to occupy the same space.

Lots of features are locked for paid membership. You can only save five designs at a time. You are limited to five image uploads (that would be a big problem for many posters). You can export to JPG but not PNG or PDF. You can only expert in “Small” size.

Some features are missing entirely. There is no “space evenly” button, paid or not.

I try a poster template. They are all 420 by 594 mm (16.5 by 23 inches). That’s really the size of a flyer to me. Too small for a conference poster.

I tried to create a poster to a custom size. Hm, can’t enter size in inches, only pixels. And the maximum number of pixels is 4,000. Too small for a conference poster.

DesignCap can’t make a conference poster. We’re done here.

Canva review

TL;DR: Canva is great for simple things like an Instagram post, but I would hesitate to use it for a conference poster.

In January (before we knew that 2020 would be a dystopian hellscape, remember?), one of my contributors mentioned making a poster in Canva. I’ve been playing around with it on and off since then, and am here to report what I've learned.

Note: All my comments are based on the free version of Canva. There is a Canva Pro that you pay a subscription fee to use.

One big advantage of Canva is that this is a cross platform app. I suspect many people will run it in a desktop web browser (which seems to be its native form). But there’s a desktop version. There are tablet and smartphone versions for iOS and Android. With an account, your work is stored online and accessible from all your different devices.

This is nice, because it means you can sketch out designs away from your desk. You can tinker with a project standing in a socially distanced line to deal with the cable company.

The big selling point, I think, is the templates. I’ve been using Canva mainly for creating Instagram posts. Here’s one I made to promote a post from a couple of weeks ago:

This was derived from a haphazardly picked Canva template, removing the text, and replacing it. For quick, small, simple things like this, I like Canva a lot.

For more complex tasks like a poster, I like it less. When you look for a poster template, the size is 18 by 24 inches. Too small for a conference poster. You can create a custom size, as long as it’s smaller than 64.5 by 38.7 inches. That is smaller than I would like, but given that many conferences seem to be trying to squash posters into smaller and smaller space, it may be all you need.

Typography is a critical point for any poster. Navigating the font selection is challenging. First, fonts you use on your desktop are not on the Canva list. No Times Roman, Arial, Gill Sans, Helvetica.

Second, the list of fonts you have is kind of huge. Forget trying to scroll through them all to find one you like.Your best bet is to search with a term like “serif,” “slab,” or “semibold.”  How these are tagged is not clear to me. I’m not sure what makes these “decorative.”

Even with a search, you are often still presented with a damn long list to scroll through.

You can upload pictures from your computer (such as graphs, etc.). But there is no serious integration with standard desktop products like Microsoft Office. You can’t upload an Excel spreadsheet and get a graph from it. You will need to make a PNG, JPG, or SVG file to import into Canva.

You cannot create guidelines. Instead, there is a lot of automatic “snap to” features that help align elements. You can also space elements evenly by selecting multiple objects.

You can create a grid, but only sort of. You click “Elements” in the left sidebar, and search for “Grid.” You don’t get a grid in the usual sense of a series of lines diving the page. Instead, you get another template that divides up the page and lets you “drop” elements into those spaces.

Here is an image with a three column “grid” with pictures dropped in.

You can resize the grid, and it resizes everything within it giving different crops.

Notice that hairline space between elements has stayed the same. I can’t see anything that allows you to set margins between elements.

As far as I can tell, you cannot set anything in Canva to a certain size. You cannot easily take an image and force it to be six inches wide, say. For an Instagram post with maybe two to four elements, that’s not a problem. For a conference poster with maybe dozens of elements, that’s a problem. You may want to make sure all your text boxes and graphs are five inches wide, for example. That’s very difficult in Canva.

Related posts

Critique: Dangerous LDL

External links

Canva

Better Posters book cover reveal!

Look at this!

The Better Posters book has moved another step being closer to reality, a blogger’s dream you can hold in your hands!

Current publication target: 25 January 2021!

Read more on the Pelagic Publishing website!