A graph to show

I’ve never been sure where “a graph to show…” comes from. As far as I can tell, A-level specifications don’t use or specify this wording, and you wouldn’t typically see it in a figure legend in a scientific paper. But if you ask first-year students to put a title on a graph without any further guidance, almost every one of them will default to this mindless boilerplate.

I hate “a graph to show how y varies with x” with a passion bordering on pathology.

“A graph to show” tells me nothing whatsoever that a properly drawn graph doesn’t already show. It is as superfluous as gold paint on a lily or jackboots on Theresa May:

• If it’s an x,y scatter-plot, then the y axis will have a clear label, stating what y is in terms that the expected audience will understand, including details of the units in which y has been measured (if any).
• If it’s an x,y scatter-plot, then the x axis will also have a clear label with the equivalent details.
• If it’s an x,y scatter-plot, then you presumably wouldn’t have plotted such a thing if you didn’t want to show me how y varies with x.
• And finally, if it’s an x,y scatter-plot, then the very last thing you should waste your breath or word-count telling me is the fact that it’s a “graph”. I know it’s a graph, because – you know – it’s got f**ing axes and f***ing data points and all the other sexy trappings of graphdom.

Titling a graph with “a graph to show how y varies with x” is a waste of time. But it’s worse that that. By training students to write mindless titles, you divert their attention from actually writing a title (and/or legend) that are useful to the reader, and to the writer.

A useful title should tell the reader enough about how (and why) the data has been collected for the graph to stand alone.

Some real(ly annoying) examples:

A graph to show how the absorbance varies with wavelength

The absorbance of what chemical? Wavelength of light, or of some other wave? How does it vary? Why should I care? Does a graph that shows absorbance (or emission) against wavelength of light have a specific name?

A graph to show how the rate of the enzyme varies with pH

Which enzyme? What substrate? How does it vary? Is there – perhaps – an optimum? What pH value gives this optimum? Is it (in)consistent with the typical pH values in which this enzyme is found?

A graph to show how the pH varies with the amount of base added to the acid

Which acid? Which base? What concentrations? Does it buffer? How many times and at what pK_a values? Is there a specific name for this experimental procedure?

A graph to show how the number of lichens in a wood varies with size

Number of lichens or number of species of lichen? Which wood? Latitude and longitude? Presumably the size of the wood, not the lichen (do you mean ‘area’?) Is there a well-known mathematical relationship between these two variables? What parameters have you estimated from it?

Writing better graph titles means really thinking about what your data show and how they were collected. Putting in the effort to give your graphs meaningful titles will result in better discussion of those results. And if you don’t…

A graph to show how your score will vary with the number of times you say “a graph to show how y varies with x”