[Eeglablist] How many clusters?

[Fran Copelli]

Dear list,

My question involves clustering when using the Kmeans algorithm. It's not
clear to me how to decide the number of clusters to compute.

In an example on the EEGLAB wiki, they suggest to cluster based on the
average amount of components per subject. However, the default number of
clusters (10) is different from the average number of clusters (20). I've
striked out a few other obvious errors in the quoted text below.

"Note that the default number of clusters (10 in this case) is set so on
average there will be one computer component per subject per cluster. For
example, if about 20 component per subjects are selected based on the
residual variance thereshold threshold and the STUDY contains 10 subjects,
the average number of cluster will be set to 20 - so each cluster will
contains contain on average 10 components."

I'm also aware of a clustering "rule of thumb" which is the square root of
(number of components divided by 2). I tried finding the source for it, and
according to online forums, there isn't a clear origin.
https://stats.stackexchange.com/questions/277007/rule
-of-thumb-on-the-best-k-in-k-means-clustering

My question is whether there is a clear rule/equation for how many clusters
to create from unclustered components from multiple subjects.

Any help is appreciated. Thank you!


Fran

SMART Lab, Psychology Department

Ryerson University