Graphs in newspapers are misleading; remove them!

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

27 February 2022

Most of the graphs that appear in newspapers are misleading. In fact, I don’t think I have ever seen one that presents the information in the correct perspective! The reason is that they hardly ever start zero and so they exaggerate the changes in the data. Newspapers zoom-in on graphs because of space constraints, but, in the process, they distort the visual effect.

I have just been looking at a graph showing the movement of the share indices at the Nairobi Securities Exchange (NSE) over the last one year. In that period, the NSE All-Share Index fluctuated between 158 and 172 points. This is a small change of just 14 points; it less than 10 per cent in twelve months.

But the vertical axis of the graph did not start from zero; it started from 150 and ran up to 180 points. On that scale, the changes in the index appears very big. The eyes see a band of 30 points (180 – 150) in which the curve fluctuates up and down over a range of 14 points. Visually, the variation appears to be almost 50 per cent.

If the same data was plotted in the correct perspective, starting from zero, the variations would be hardly noticeable. Such a graph might appear dull and uninteresting. This graph was about 5cm (50mm) in height. If the vertical axis started from zero and ran up to 180, then each millimetre would represent 3.6 points.

On that scale, the 14 points between the highest and lowest level of the index would be seem as just 4mm – barely discernible. On the other hand, when the scale is changed to run from 150 to 180 (a range of 30 points), each millimetre will now represent 0.6 points. Consequently, the 14-point fluctuation will be almost 24mm (2.4cm – almost one inch) on the graph.

If you are thinking that 2.4cm is small, that’s because you have forgotten that it is in a graph that is just 5cm tall! That is, the fluctuation is about a half of the entire graph! That is, it is grossly exaggerated.

The question then arises: are the graphs necessary? In most instances, I don’t think they are. And, since they are misleading most of the time, I would recommend doing away with them altogether!