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David McQuillan
This little article is for those who want to know how I calculate a difficulty rating for dances. My rating isn’t particularly wonderful compared to that in Keith Napier's Index, which by the way gives a difficulty rating for about 5000 dances, but it is an attempt to automate the whole process.
Basically the assumption is that every event has an overall difficulty rating. This can be assessed from that of the dances in the event. Then in a recursive fashion the difficulty rating of the dances can be assessed from that of the events they are in. The whole process is kick started by putting in the Napier Index rating where possible.
This is a work in progress so it will change!
I assume events have a difficulty spread which differs from event to event. The assessment of the difficult of a dance also has a variance which must be gauged from that of the events they are in.
The difficulty level of a dance is given as:
Sum of (mean/variance) for the events the dance is in / Sum(1/variance) for the events the dance is in.
This has to be normalised by expanding the range as it would all tend towards the mean.
For each event the mean and variance is given as the mean of the dances in it and the straightforward sum square difference from the mean divided by the number of dances used.
In fact I also currently use the variance of the dances in assessing that of the events to bump up the overall variance. It probably would be easier and better to just add some fudge factor so a very small variance doesn’t have too big an effect.
Currently most of the progammes come from the Summer Tuesdays SCD email list. The dances are recognised using a Double Metaphone matching algorithm
The simpler dances don’t tend to be on published programmes.
The most popular dances appear to be less difficult than they are intrinsically because it is assumed people know them. It may be possibe to do some adjustment dependng on the popularity of a dance (i.e. how often it is in programmes). On the other hand it may be that this effect is actually desrable.
The less popular dances may easily have their difficult assessed from only one or two events. I should try to get programmes from a wider area to avoid this effect to some extent.
No account is taken of the position of dances in a programme. It may be possible to do something about this:
Clubs tend to a difficulty level and especially the same event by a club in successive years.
The maths could be greatly improved! It is only faith that leads me to believe the whole process works. I hope to run some rank order tests compared to Napier to check it out. It'll also be interesting to start with some random numbers, iterate a few times, and see if the result correlates with difficulty.
Another way of assessing difficulty automatically is to use the length of the description of the dance in MiniCrib. I’ve been considering using a variant where the dances are compressed so frequently occurring phrases take up less space, e.g. cross, cast, half figure of eight.
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