I have a dataset that I am analysing to find the optimal number of clusters using k-means.
I am testing the number of clusters from [1..11] - which produces the following plot:
The original dataset has six classes but the elbow plot shows the bend really occurring at 3 clusters. For curiosity I overlaid a line on the plot from 11 clusters and back and it is almost a straight line to 6 clusters - which indicates to me that the real elbow is at 6, but it is subtle to see.
So, visually 3 looks to be the right answer, but given the known number of classes (6) the straight line I drew indicates 6...
- How should you correctly interpret an elbow plot like this (especially when you are not given the classes)?
- Would you say the elbow is at 3 or 6?