Beware dodgy axes (on graphs, not chopping wood)

Every now and then I feel the need to remind people that whenever you see a graph you should take a look at the axes (I'm thinking of the plural of axis here, not of axe - though it probably is wise to keep an eye on axes too). If you want to make some data look far more dramatic than it really is, it is possible to do this very easily by only using a small part of the available vertical axis.

Today, I noticed a graph published by the Spectator magazine. I have nothing against the Spectator - I don't always agree with its politics, but it is a good read. However, this particular graph was egregious in its axis mangling. The intent was to demonstrate the impact that the speech given by Rachel Reeves (UK chancellor at the time of writing) on 4 November had on the pound/dollar exchange rate. It looked like this:

Wow. That's a dramatic fall. But look at that horizontal axis. For a comparison I plotted roughly the same data (roughly as it's just read off the graph by eye) with an axis that starts at zero. It looks like this:

(The vertical axis markers are missing as I was simply taking equal left to right measurements by eye, rather than pinning down to a specific time). There is still a drop. But you do need a magnifying glass to notice it.

Sometimes it can be helpful to only take part of the range from the vertical axis, but it shouldn't be done in such a way to make a change seem dramatic when, frankly, it isn't.

These articles will always be free - but if you'd like to support my online work, consider buying a virtual coffee or taking out a membership:

See all Brian's online articles or subscribe to a weekly email free here

Comments

Why I hate opera

If I'm honest, the title of this post is an exaggeration to make a point. I don't really hate opera. There are a couple of operas - notably Monteverdi's Incoranazione di Poppea and Purcell's Dido & Aeneas - that I quite like. But what I do find truly sickening is the reverence with which opera is treated, as if it were some particularly great art form. Nowhere was this more obvious than in ITV's 2010 gut-wrenchingly awful series Pop Star to Opera Star , where the likes of Alan Tichmarsh treated the real opera singers as if they were fragile pieces on Antiques Roadshow, and the music as if it were a gift of the gods. In my opinion - and I know not everyone agrees - opera is: Mediocre music Melodramatic plots Amateurishly hammy acting A forced and unpleasant singing style Ridiculously over-supported by public funds I won't even bother to go into any detail on the plots and the acting - this is just self-evident. But the other aspects need some exp...

Is 5x3 the same as 3x5?

The Internet has gone mildly bonkers over a child in America who was marked down in a test because when asked to work out 5x3 by repeated addition he/she used 5+5+5 instead of 3+3+3+3+3. Those who support the teacher say that 5x3 means 'five lots of 3' where the complainants say that 'times' is commutative (reversible) so the distinction is meaningless as 5x3 and 3x5 are indistinguishable. It's certainly true that not all mathematical operations are commutative. I think we are all comfortable that 5-3 is not the same as 3-5. However. This not true of multiplication (of numbers). And so if there is to be any distinction, it has to be in the use of English to interpret the 'x' sign. Unfortunately, even here there is no logical way of coming up with a definitive answer. I suspect most primary school teachers would expands 'times' as 'lots of' as mentioned above. So we get 5 x 3 as '5 lots of 3'. Unfortunately that only wor...

Why backgammon is a better game than chess

I freely admit that chess, for those who enjoy it, is a wonderful game, but I honestly believe that as a game , backgammon is better (and this isn't just because I'm a lot better at playing backgammon than chess). Having relatively recently written a book on game theory, I have given quite a lot of thought to the nature of games, and from that I'd say that chess has two significant weaknesses compared with backgammon. One is the lack of randomness. Because backgammon includes the roll of the dice, it introduces a random factor into the play. Of course, a game that is totally random provides very little enjoyment. Tossing a coin isn't at all entertaining. But the clever thing about backgammon is that the randomness is contributory without dominating - there is still plenty of room for skill (apart from very flukey dice throws, I can always be beaten by a really good backgammon player), but the introduction of a random factor makes it more life-like, with more of a sense...

Search This Blog