Cha-cha-charts – Strictly statistics part 1

I don’t watch Strictly Come Dancing. All those sequins and dazzling teeth, the bright lights and the whooping audience. It’s not for me.

But my interest has been piqued by a Radio Times article on what the numbers might predict would be the likely winner. They’ve taken a look at average (mean) scores, variation in performance standard, and recent form to have a punt at who will grab the title.

That sort of thing is the bread and butter of statisticians. Though usually it’s for things such as medical research or industrial quality control.

And statisticians have lots of sophisticated, mathematical techniques to work with. Their analyses can help answer questions such as we seeing a trend or blip; are the improvements real, or will there be regression to the mean?

Whatever your statistical skills it’s always a good idea to start with a visualisation. Plotting the numbers can really bring out their key points.

So let’s have a look at how the surviving celebrities (as at week 10) have done.




The charts show the total of the judges’ scores on the y-axis against the week number of the series. The source for scores is the web site

All the contestants appear to have seen a trend towards improvement – some steady, others more erratic.

Let’s have a look at all of them together:


You’ll see that I’ve chopped off a lot of the scores axis (the y-axis) as none of the contestants was scoring very low. This highlights the week-by-week variations. The advantage of not chopping the y-axis is that it seems to be easier to see the trend.

Does this mean that these contestants started with a similar level of skill, diverged as they took more or less time to learn the skills, and are now reaching a peak which is about the same for all?

What questions can we ask about past performance that might give us a clue to future performance?

I’ll be returning to this topic soon. In the meantime: remember, keep dancing!

And, if the chart above looks like someone’s been meddling with the London Underground map, have a look at this! It’s the chart for all contestants.



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