Posts filed under Graphics (346)

January 18, 2016

Meet Statistics summer scholar Oliver Stevenson

Oliver StevensonEvery summer, the Department of Statistics offers scholarships to a number of students so they can work with staff on real-world projects. Oliver, right, is working on visualising conservation data with Associate Professor Rachel Fewster. Oliver explains:

“This summer project is called Maps, graphs, and data analysis for community conservation projects, and builds on my Honours project from the past year. It involves developing interactive applications that automate the display of catch data from various conservation projects around New Zealand.

“The aim of this project is to allow volunteers to engage with their data in more depth than ever before. After a day in the field, a conservation volunteer is able to go online and use these applications to produce maps or graphics to view their day’s work. The graphics illustrate exactly how a volunteer’s work is impacting their local environment and will ideally keep them motivated to continue with what they are doing.

“I graduated from the University of Otago in 2014 with a Bachelor of Science majoring in Statistics and minoring in Psychology, before completing an Honours degree in Statistics at the University of Auckland in 2015. In 2016, I plan on pursuing a Master of Science in statistics, completing this degree as a research masters.

“I enjoy statistics due to its numerous applications. Nowadays, data exists in almost every facet of life, and wherever there is data, we can use statistics to try and gain a deeper understanding of what is really going on around us.

“In my spare time this summer, I will, hopefully, be able to watch the Black Caps as they continue with their summer of cricket.”



January 15, 2016

Meet Statistics summer scholar Hubert Liang

Every summer, the Department of Statistics offers scholarships to a number of students so they can work with staff on real-world projects. Hubert, right, is working on ways to graphically represent community conservation effHubert Liangorts with Associate Professor Rachel Fewster. Hubert explains:

“Conservation efforts are needed to protect the natural flora and fauna of our beautiful country. This exciting project involves preparing and analysing data collected from volunteers involved in conservation efforts against pests such as rats.

“The data is analysed and uploaded to a website called CatchIT, which is an interactive website that allows the bait and trap information to be presented in graphic form to volunteers, which provides feedback on their pest-control efforts. The data comes to life on the screen, and this engages current and future volunteers in tracking the success of their pest-control projects.

“I am in the final year of my Bachelor of Science majoring in Statistics and Biological Science, having previously finished a Bachelor of Pharmacy (Hons). Statistics has a wide applicability to a wide range of disciplines, and appeals to me because I am passionate about the simple process of getting the most from raw data. It is a very rewarding process knowing that you can make the data more appealing and important to the end user.

“This summer, besides doing this studentship, I’ll be enjoying the sunshine, and relaxing on the beach with family and friends.”


December 23, 2015

Pre-attentive perception and pandas

The University has closed until the New Year and we are on compulsory holiday, so from my point of view it’s the StatsChat Silly Season.

An important scientific issue in designing graphics is preattentive perception: for example, it’s easy to see the one different point in this plot

The circle vs triangle distinction is pre-attentively perceived: your visual system annotates it before you get to see the picture.  More complicated distinctions aren’t pre-attentive, and so don’t make as good plotting characters.

Here, as a Christmas card, is a picture from Hungarian cartoonist Gergely Dudás. One of the snowmen is a panda. Pandas are not pre-attentively perceived.


(update: yes, I saw the Herald has it too.)

December 15, 2015

Graphs: when zero is not a relevant value

Bar charts have a filled area tying the axis to the plotted value, and this only makes sense when the axis is at a true zero.  Scatterplots and line plot don’t have the same limitations, and can be useful even when there isn’t a true zero or it isn’t a relevant value.

Here’s the Wikipedia compilation of world average temperature estimates back into deep time:


The zero on the graph is the 1960-1990 average, because that’s a reasonable point of comparison. It’s not a true zero; you couldn’t use barcharts.

Here’s the Berkeley Earth estimate of average land temperatures, based on actual thermometer readings at weather stations, using all the data, with open code, data and methods.


They could have put a zero on the graph by using differences from the average for some period — their data output is difference from the 1951-1980 average — but they presumably thought it was clearer to just label in degrees Celsius and not make everyone do the conversion.

We had a comment suggesting that zero Celsius should be on this sort of graph, and there’s a graph circulating on Twitter that has its baseline at zero Fahrenheit.


These looks like a deliberately uninformative choice: there’s nothing special about zero Fahrenheit and nothing special about zero Celsius as temperatures either in any absolute sense or as mean global temperatures.

The only natural zero for temperature is zero kelvin. If you want to argue there has to be a zero on climate graphs, it should be that one. But you’d look silly.

If you want to use graphs of temperature history to make a point about policy, the graph needs to be one where differences that would matter for policy are clearly visible. As far as I know, no-one denies that a rapid 4C (7F) change in global temperature would be important. If your graph would make it look unimportant, your graph is wrong.


December 9, 2015

Not how barcharts work

From the @nzlabour twitterwallah, via Matt Nippert


Barcharts start at zero. Other sorts of charts don’t need to, but barcharts do. A line chart cut off at $300 would be ok — though if you were going to do that, you might as well include a longer range of data.

For example, here’s the top couple of inches of the detailed graph from Herald Insights, with the jump under Mr Smith’s administration highlighted in yellow.


Or you might compare to the increase in median household income for the Auckland region over that period, which was about 9%, and say that affordability of rental housing has decreased by maybe 5% over that time period.  Or compare to the increase in minimum wage (7%). Or something.

Representing a time trend for which there’s weekly monthly data by a two-point decapitated bar chart suggests a low opinion of your audience. When Fox News does it, that’s fair enough, but from a New Zealand political party it’s unfortunate.



November 18, 2015

Old-time graphics advice

  1. We must keep symbols to a minimum, so as not to overload the reader’s memory. Some ancient authors, by covering their cartograms with hieroglyphics, made them indecipherable.”
  2. “One of us recommends adopting scales for ordinate and abscissa so the average slope of the phenomenon corresponds to the tangent of the curve at an angle of 45◦”.
  3. “Areas are often used in graphic representations. However, they have the disadvantage of often misleading the reader even though they were designed according to indisputable geometric principles. Indeed, the eye has a hard time appreciating areas.”
  4. “We should not, as it is sometimes done, cut the bottom of the diagram under the pretext that it is useless. This arbitrary suppression distorts the chart by making us think that the variations of the function are more important than they really are.”
  5.  “In order to increase the means of expression without straining the reader’s memory, we often build cartograms with two colors. And, indeed, the reader can easily remember this simple formula: ‘The more the shade is red, the more the phenomenon studied surpasses average; the more the shade is blue, the more phenomenon studied is below average.’ ”

These are from a failed attempt to get the International Institute of Statistics to set up some standards for statistical graphics. In 1901.

(from Hadley Wickham)

November 13, 2015

Flag text analysis

The group in charge of the flag candidate selection put out a summary of public responses in the form of a word cloud. Today in Insights at the Herald there’s a more accurate word cloud using phrases as well as single words and not throwing out all the negative responses


There’s also some more sophisticated text analysis of the responses, showing what phrases and groups of ideas were common, and an accompanying story by Matt Nippert

Suzanne Stephenson, head of communications for the flag panel, rejected any suggestion of spin and said the wordcloud was never claimed as “statistically significant”.

“I think people misunderstood it as a polling exercise.”

“Statistically significant” is irrelevant misuse of technical jargon. The only use for a word cloud is to show which words are more common. If that wasn’t what the panel wanted to do, they shouldn’t have done it.



November 9, 2015

Inelegant variation

These graphs are from the (US) National Cable & Telecommunications Association (the cable guys)


Apart from the first graph, they are based on five-point agree-disagree scales, and show the many ways you can make pie and bar charts more interesting, especially if you don’t care much about the data. I think my favourites are the bendy green barchart-orbiting-a-black-hole and the green rectangles, where the bars disagree with the printed numbers.

Since it’s a bogus poll, using the results basically to generate artwork is probably the right approach.

To each according to his needs

There’s a fairly overblown story in the Guardian about religion and altruism

“Overall, our findings … contradict the commonsense and popular assumption that children from religious households are more altruistic and kind towards others,” said the authors of The Negative Association Between Religiousness and Children’s Altruism Across the World, published this week in Current Biology.

“More generally, they call into question whether religion is vital for moral development, supporting the idea that secularisation of moral discourse will not reduce human kindness – in fact, it will do just the opposite.”

The research found that kindergarten (update: and primary school) children from religious families scored lower on an altruism test (a version of the Dictator game).  Given ten stickers, non-religious children would give about one more away on average than religious children.


While it’s obviously true that this sort of simple moral behaviour doesn’t require religion, the cause-and-effect conclusion the story is trying to draw is stronger than the data. I’m pretty confident the people quoted approvingly wouldn’t have been as convinced by the same sort of research if it had found the opposite result.

The research does provide convincing evidence on another point, though: three-dimensional graphics are a Bad Idea.



October 22, 2015

Early NZ data visualisation

From the National Library of New Zealand, via Jolisa Gracewood


Types of motor-vehicle accidents in rural areas vary considerably from those ocourrlng In urban areas, as shown in tho above chart. Tho percentages are based on figures of the Transport Department in respect of accidents causing’ fatalltles during the twelve months, April I, 1932, to March 31, 1933.

The text goes on to say “The black section representing collisions with tram and train forms only I per cent, of the whole, through this type of accident appeals to the popular Imagination’ from its spectacular nature.”  Some things don’t change.