NbClust for YAML-500 (2-250 clusters)

Ball_Hall

The mean, through all the clusters, of their mean dispersion.
The range is [0,+∞).
The difference between two successive slopes to be maximized.

C_Index

Shows for a given clustering its fraction of maximal possible increase over minimal distances which within-cluster distances between pairs of points have.
The range is [0,1].
To be minimized.

Calinski-Harabasz

Is proportional to the quotient of the between-group dispersion and pooled within-cluster dispersion.
The range is [0,+∞).
To be maximized.

McClain_Rao

Is the quotient of the mean within-cluster and between-cluster distance.
The range is [0,+∞).
To be minimized.

Ratkowsky_Lance

Is based on the mean of the quotients between between-group dispersion and TSS for each variable of the data.
The range is [0,+∞).
To be maximized.

Davies-Bouldin

Deals with those clusters which are “close” in terms of their barycenters to each other but have very distant points within.
The range is [0,+∞).
To be minimized.

Silhouette

Operates with quantities that only depend on the average distances between a given observation and other observations inside its own and also inside the nearest cluster.
The range is [0,1].
To be maximized.

Dunn

Deals with those clusters which contain the closest points belonging to different clusters and also with clusters that have very distant points within.
The range is [0,+∞).
To be maximized.