Graphs: a how to guide

How to avoid any graph gotchas...
18 December 2020

Interview with 

Nira Chamberlain, Institute of Mathematics


A pie chart graph


Thanks to the pandemic the eyes of the world have been on various graphs representing cases, tests, and all sorts, but there are some common tricks in the graph making-trade to be aware of, as Adam Murphy heard from Nira Chamberlain, the president of the institute of mathematics, earlier this year...

Nira - One of the most common ways to actually manipulate a graph is, let's say you have a bar chart and you want to see how much profit you're making beyond your competitor. Or you want to show that, you know, your product is much better than your competitor. So let's say my product makes you a hundred pounds saving while the competitor only makes a 95 pound saving. So one of the ways of actually manipulating this is actually to compress the vertical axis so that it actually only starts from, let's say, ninety and ends at a hundred. So when you actually look at that, it looks like your profit is twice as much than your competitor, without realising that actually the chart should go all the way down to zero. So that's a common practice that people do.

Adam - What tips would you have for people on how to read graphs effectively? Say someone sits down and they see a graph in a newspaper, what's the best way of going about reading and understanding and not being fooled?

Nira - The key thing is one, look at the Y axis, does it go up sequentially, or does it go up geometrically? So is it a log scale. Second, every graph should have a source. You know, they say this is taken from a source, but also actually look at the date which the graph was done. I mean, sometimes people will quote you statistics, but the statistics are actually out of date. So what's the best thing to do is look at the Y axis and look at the source and look at the date from when this statistic was actually produced.


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