2017-12-07
[public] 101K views, 3.13K likes, 94.0 dislikes audio only
Jen Rogers is a statistics researcher and lecturer at the University of Oxford.
https://www.jenniferrogers.co.uk/
We chat about how the scoring system works on Strictly Come Dancing (“Dancing With the Stars” in the USA and other countries). The UK system for dealing with ties is unfair!
Jen and I do Maths Inspiration shows together.
http://www.mathsinspiration.com/
We’re out doing The Curious Coincidence of Maths in the Daytime in Melbourne next February.
https://www.artscentremelbourne.com.au/whats-on/2018/education/curious-maths-in-the-day-time
Results from Judges votes Saturday 2 December 2017
Joint first: Alexandra & Gorka
Joint first: Debbie & Giovanni
Second place: Joe & Katya
Third place: Mollie & AJ
Joint last: Gemma & Aljaž
Joint last: Davood & Nadiya
http://www.bbc.co.uk/blogs/strictlycomedancing/entries/34fb3f42-2210-4080-a01f-962719269386
After being combined with the audience rankings the bottom two were Alexandra & Gorka and Davood & Nadiya. But if the ties were done properly that could have been Gemma & Aljaž instead of Alexandra & Gorka.
If you have a way to get us the data from the BBC, send me an anonymous email! matt@standupmaths.com
CORRECTIONS:
- Shimassi and others have made very important points about how this system favours the public vote. Because a tie means the judges accidentally give extra points to the contestants they’re trying to rank at the bottom.
This is my fault for not being clear enough. When we said things like “skewing it towards the judges” and “inflating the judges’s score” we are talking about there being more points being given. Not that the judges were getting their way. Sorry I did a bad job of talking about that and my language was not precise enough.
Jen’s main example was that the contestant ranked top by the judges was unfairly moved to the bottom two (and into the dance-off) because the public got their way.
In short: the audience can always penalise someone by given them one vote, the judges can’t always do that.
Another interesting fairness metric is that someone top-ranked by the judges and bottom-ranked by the audience should be exactly equal to someone bottom-ranked by the judges and top-ranked by the public. But if there is a tie for the judges the audience choice gets an unfair advantage.
- Others have pointed out (and David Heath sent a great email to me) that Strictly once had a system like what we describe but they got into trouble because people were paying to phone in and vote for a contestant when it was mathematically impossible for them to be voted out of the dance-off. And the BBC can’t have a phone-in competition if some votes cannot make a difference.
This makes for an interesting set of criteria. The voting system needs to be fair, easy to explain to a TV audience and the audience vote is always able to move any given contestant out of the bottom two.
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Design by Simon Wright
MATT PARKER: Stand-up Mathematician
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