If we as journalists are sometimes nervous about numbers, then just think how much more difficult it is for our audience to make sense of the data we give them.
It's as if, in our anxiety to get the numerical part of a story over with as quickly as possible, we hurl gobbets of undigested data at our unsuspecting readers in the hope that some of it will stick.
We wouldn't do it with any other part of the story. How many times does a newsdesk pull up a reporter on gaps in the chronology, inconsistent spelling of names, unexplained acronyms? Yet errors in basic maths still slip through. We don't expect our readers (or viewers, or listeners) to fill in gaps in chronology or narrative for themselves; so why should they suddenly be assumed to have near-psychic powers when it comes to divining our intention as to the meaning of 'average', or determining the sample size of a survey, or the size of a budget cut?
But there are five basic rules which can make life much easier for our audience when it comes to reporting with figures. These are mainly aimed at print journalists but apply to TV, radio and online as well:
1. Do the hard work for them: The press release from your council says council tax for a typical property will go up by 3.5 per cent next year, from £1,215. Skipping over the question of how 'typical' has been defined, homeowners will want to know how much cash they will need to stump up next year. They shouldn't have to reach for the calculator - that's your job (and it's £1,257.53, by the way).
Don't leave readers with unanswered questions based on figures in your story; do the maths for them.
2. Know when to round off: In the council tax example, I rounded off the true answer of £1,257.525 on the basis that the 1p is the smallest denomination coin, so talking about '52 and a 1/2p' doesn't make sense. Or suppose local anglers are furious that river pollution has led to 20 per cent fewer fish being caught, down from 83 last month. A decrease of 20 per cent is 16.6 fish, but since no one has ever caught 0.6 of a fish, we'd have to say 'that's 17 fish fewer than last month'. In other cases, the full figure might make sense but is over-precise.
If the total amount misclaimed by UK MPs for their expenses turned out to be £1,000,102.13, nothing is lost by rounding this to 'just over £1 million'; that extra £102.13 doesn't make it any more shocking. There is no hard and fast rule for when to round off. It is unusual to show more than one decimal place, but in cases where the precise figure is the story, then you might need to quote the full figure.
You need to make a judgment call - how significant is this figure to the story? What is lost if the figure is rounded off? If you do round off, remember it can lead to small errors in adding, so explain this: "Rounding means percentages may not add up to 100."
When you do decide to round off, the rule is to look at the part you are about to throw away - if it begins with four or less, then just discard it; but if it is five or more, then increase the final digit of your rounded number by one. As an example, 14.39 rounded to a whole number is 14 (because we are discarding '.39', which starts with '3'); but 172.91 becomes 173, because we are discarding '.91', which starts with a '9'.
Never, ever work with rounded figures if you need to do calculations - always use the full, accurate number and only round the result.
3. Tame extreme numbers: Numbers which are very large or very small can be difficult to visualise and comprehend, so put them onto a human scale. Here's an example I use on my News Numeracy blog: say the local medical college has discovered a new microbe and calculates there are around 100,000,000,000 of these microbes on earth - you want to include this in your article, but who has any intuition of how large that number is?
Therefore you relate it to something readers are at home with: there are around 3,000,000,000 (three billion) seconds in a century, so you can report, 'If you counted three of these microbes every second, it would take you 100 years to count them all'.
Note that the UK now follows the US by defining a 'billion' as 1 followed by nine zeros; it used to be 12 zeros.
4. Numbers numb: You can have too much of a good thing, so don't overload the story with data. As a rule of thumb, use no more than three numbers per sentence, including ages, dates and house numbers. Where appropriate, summarise figures or use analogies to avoid numerical over-load. Percentages and averages are often more useful than raw figures, because they can put things into context.
But on the other hand, don't skimp on key information, which brings me to the final rule...
5. Give the full story: There is a temptation, particularly in radio reports, to gloss over figures as inherently dull - and certainly no one would suggest cramming a 30-second radio bulletin with dozens of digits. But it often only takes one short phrase to add the all-important rider that, 'This poll has a 5 per cent margin of error', or 'That's an increase of 8 per cent'.
Graphs are often an effective way of displaying otherwise complex figures, in which case radio stations can refer listeners to their website for more information. TV news generally handles the presentation of numbers well, despite the tendency to STBO ('show the bleeding obvious') - someone tell Peter Snow that I really can imagine what it would be like for the Tories to win 405 seats without the need of a colourful 3D model of the Commons to drum the fact home.
But the web is undoubtedly where data presentation comes into its own - interactive charts, timelines, collaborative reporting, animated graphics and full access to original spreadsheets are just some the advantages offered online. Why any news organisation wouldn't offer an online interpretation of stories involving a lot of figures is beyond me.
In addition to the basics above, each news organisation will of course have its own house style for the way in which figures should be presented and formatted.
As always, the key is to be kind to your readers; let the numbers illuminate the story, not obscure it.
Steve Harrison is a journalism lecturer at Liverpool John Moores University, having spent most of his working life as a journalist with the Liverpool Daily Post and Echo.
An Oxford graduate in English, Harrison began his career at the Winsford Guardian in 1983 before moving to the Post and Echo in 1986, where he was variously a reporter, sub-editor and online editor. His last role there was as acting assistant editor (digital), responsible for running the websites of both the daily titles.
He also has an interest in newsroom numeracy - so much so, that he is due to complete a BSc in Mathematics with the Open University later this year. He blogs on the subject at Newsroom Numeracy.
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