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Page last updated at 12:18 GMT, Wednesday, 11 March 2009

How to understand risk in 13 clicks

Different ways of seeing stats

Michael Blastland

What are we to make of all those stories that warn of lifestyle dangers and slap a giant "%" sign in the headline? Michael Blastland introduces the Risk-o-meter to his regular column.

In response to your e-mails after the last column, and the everyday fog of statistics about risks, I've produced what I hope is a better way to see the numbers.

From bacon to booze, risks often make headlines: "CANCER UP X PERCENT IF YOU DO Y" - you know what I'm talking about. So I've devised a simple but different way of seeing stories, with a click-by-click Risk-o-meter. Click through the examples below to see why those percentages easily mislead - and why it pays to ditch percentages and talk instead about the numbers of real people.


Bacon increases your risk of colorectal cancer by 20%
But how bad is that?
About 5 people in 100 have colorectal cancer in a lifetime
If all 100 eat three extra rashers of bacon every day, that rises to about 6
That's the same as saying one extra case in every 100 people
One extra unit a day increases a woman's risk of breast cancer by 12%, but how bad is that?
About 10 in every 100 women have breast cancer in a lifetime
If all 100 drink an extra unit of alcohol every day, that rises to about 11
That's the same as saying one extra case in every 100 women
Two units a day reduce the risk of heart disease by about 17%, but how good is that?
About 32 in every 100 have coronary heart disease in a lifetime
If all 100 drink roughly two units of alcohol every day, that falls to about 27
That's the same as saying about five fewer cases in every 100 women
So depending on the story, number changes. Don't think percentage, think real people
{current} of {total} NEXT BACK

Two caveats. First, links between a food and a health hazard (or benefit) do not always indicate a direct cause. Second, some studies have produced different numbers to the ones here. The benefit of moderate alcohol, for example, is at the conservative end of estimates. Some studies suggest it can be far more beneficial.

We'll bring out the Risk-o-meter if stories like these have drifted into abstract meaninglessness and we'll convert them into something more human.

To be fair, governments and epidemiologists (people who study patterns of illness and their causes) do need to know the percentages - but don't need the media to tell them. The rest of us, who might rely on the news for guidance, deserve something more relevant.

• Go Figure hopes from time to time to bring you arresting ways of seeing data. How the numbers look often changes how we understand them. New ideas for data visualisation - like animation in graphs - are causing a buzz among people who use lots of stats, among them the news media. Not everything we offer will be cutting edge, but we hope it will stimulate.

Here's an idea (see image below) called parallel sets, designed to show data with categories that divide into other categories. This one shows passengers on the Titanic, male and female, by class of ticket, and by survival, and is designed by Robert Kosara of the University of North Carolina. Take a moment to explore it and let us know what you think.

Titanic graphic

Below is a selection of your comments.

Brilliant!- I work as a CFO of a bank and this graph would be ideal in understanding risk across a portfolio for example. You could depict numerous dimensions on a single page rather than labor through the numerous tables dissecting the data.. Would definitely use it at my workplace!
Thomas George, Kuwait

This graph is a very rich in information and provides terrific comparisons. It reveals so much about the times. I'd love to see one like this on newspaper front pages explaining wealth distribution, health care and insurance in the USA, contributions to and extent of environmental change...etc.
Pete, Portland, Oregon

What an excellent series of articles - I never knew they existed! It's especially good to see these on the BBC site as, I'm afraid to say, the BBC are often rather casual in their approach to science reporting. Thanks for that.
Ian Gray, Brighton, UK

It seems a bit bias to only look at colorectal cancer, breast cancer and coronary heart disease. It is possible to pick the diseases accordingly so the outcomes turn out in favor/against, when comparing percentages to numbers. What about the +/- effects of alcohol on all other sorts of diseases? For it to be relevant for the average person like myself, it would make sense to look at the +/- of alcohol and bacon relative to all cancers/diseases in general as oppose to 2 or 3.
Emad, Calgary, Canada

As a visual learner I thought this was a very clear and easy way to read and understand the data. Brilliant!
Sue Baker, Leek, GB

This is the first time I've seen this way of representing sets, and it's nicely intuitive. However, the vertical axis introduces a mental bias - the impression that travel class was the most influential factor in outcome, which may or may not be true, given the information displayed. I also would suggest it would make more sense to keep the most coincident sets lined up vertically ie: move the male dominated crew category to the far right and move the survived category dominated by females to the left.
Lisa K, Durham NC

My first impression was "What a mess!" - it is not immediately clear what is being shown, and we are used to "a picture being worth..." But after spending some time on it, I was shocked to see that almost no second class men survived, while almost all first class women did. I'm still not convinced that this one diagram is preferable to three diagrams concentrating on sex v class, class v survival, and sex v survival.
Roy Sayers, Leeds

In looking for clear and concise methods of communicating quantitative data I'd suggest looking at Japanese books and newspapers. Their level of maturity in the use of graphical techniques is way better than ours, and they have many great ways to communicate in diagrams and figures. My experience is that the Japanese public are much more educated in the use of graphs and visual aids, and we could learn a lot from them.
Peter Cumpson, Newcastle-upon-Tyne

Ooh, I like this - it makes me really think about what this image is trying to convey. Rather than just skimming my eyes over another bar graph. This tells us things like a majority of the male crew did not survive, and about half of the female crew members perished. I just realised that I can't stop thinking in percentages though - must be the lack of numbers.
Hena Faqurudheen, Mumbai, India

I applaud you innovative risk visualisation approach. I have seen friends and family drop needed medications or change diets because of a news story that discusses substantial percent risk changes that only if you investigate turn out to be changes in low overall risks. Your idea of displaying overall risk is right on and might help people key in on changing behaviour related to their highest overall risk factors. Bravo.
John Shanklin, Shoreham, New York

It is visually a beautiful graph but lacks an immediate content message. It may work for technical presentations, but not for the average reader. A graph should help CLEARLY and QUICKLY convey a message better (or more efficiently) than text would. This is asking too much of the reader because it takes too much time to understand the message. It may work for a technical paper where you are interested in the analysis, but not necessarily in a mass-media publication where the reader is largely interested in gaining awareness.
Ruben Moreno, Oakton, VA USA

Florence Nightingale's original pie charts were much easier to read than this.
Caroline Keef, W Yorks

Really like the parallel sets graph, took me about five seconds to work it out, then I realised it's a really good way to present complex data sets. When will my spreadsheet software be able to produce one of these for me?
Simon, Bristol, UK

I have absolutely no idea how to read that graph. My guess is as follows - it looks at though possibly the highest percentage of survivors within a group/class is if you were travelling in first class (looks as though roughly a third, or just under a half survived)?
Paul Spargo, Cardiff, Wales

I took a little time to understand the image. It is so unlike any data presentation I personally have seen before that my first reaction was to be puzzled. After a minute or two to read the headings, it wasn't at all hard to understand and I thoroughly enjoyed following the various strands. I found it gave me a lot more information in one place that I normally see in reports and gave me the opportunity to start linking variables together and getting a better overall picture of the data.
J Howe, Bolton UK

I like the way you can look at the dynamic from different perspectives like "what type of people survived" or "did all of first class survive and everyone else perish". A surprise for me is the sheer numbers of crew compared to passengers and the chances of survival of a male first class passenger was about 1 in 4. Remarkable way of showing the data and engages debate. I think I'll take a copy.
Dave Tyrer, Leeds

Visualisation is the key to understanding complex (and somewhat obscure) dataset, especially in statistics. This graph demonstrates that if you really want to commute by Titanic you better be female and pay an hefty fee for your ticket.
Armando Forlani, London

It took a moment to understand the Titanic chart but once it "clicked" it made good sense. Its hard to put that much data in one chart and it was an intelligent and clever way to do it. I also liked the way the risk data was presented in the story. Risk is sometimes a difficult subject to explain as there is often more than one reason for the outcome (similar to the Titanic data).
Joel Baumbaugh, San Diego, California

I remember a geography professor in a lecture deliberately misusing statistics: "70% of Finland is forest & 35% of Finland is water. This does not leave much room for the Finns."
Duncan Peet, Edinburgh

Great way to show stats. But how about actual figures? It tells me that third class male passengers were way more than female passengers and most of them did not survive. But there is no clue as to how many male passengers actually survived. Don't parallel sets display actual figures and numbers?
Sourav Basu, Salt Lake City, Utah

Very interesting way of showing multi-faceted data. Takes a little time to figure it out but worth the effort. It would be improved if you could mouse over or select in some way so that one group became highlighted. Or perhaps show the numerical data in a similar fashion?
Geoff, Caledon, Canada

I studied statistics as part of my degree in the late 70s, qualified as a chartered accountant and am now a finance director. All this has taught me to ask the right questions when statistics are quoted at us. Too few people question, or are in a position to question the stats. What questions were asked? What was the population? What was the sample? Is the pronounced interpretation of the result the only one that can be placed upon it? I have now got my children questioning the information they are fed: and this is where education really needs to get children thinking, so that they ask the right questions and not just repeat the information given as if it is "the truth". As for this chart, it took some understanding but I liked it and it is a useful way of showing certain types of multi-layered data in a two-day chart. Interesting.
Richard Wyatt, Huntingdon, Cambridgeshire

Interesting article proving that percentages really mean nothing unless put it to context. Every week a new statistic (normally as a percentage) comes out telling us we are all going to die sooner, but as shown above the effect is normally very small on a personal level. On another note the parallel sets diagram is an amazingly concise way of showing the data, I may start using it myself.
Aly, Scotland

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