In cluster analysis, this measure combines the notions of cluster cohesion and cluster separation for a given observation. Which of the following is INCORRECT about this measure?

a$.$ Negative values represent weak cluster separation, and the observation is closer to a different cluster than its own.

b$.$ Its values range from $-1$ to $+1$

c$.$ It is one of the many metrics that allows assessment of the clustering method.

d$.$ A larger value represents weak cluster cohesion and a better match between an observation and its own cluster.