Editing Cluster analysis (section)

==== Chi Index ====
The Chi index<ref>{{Cite journal |last1=Luna-Romera |first1=José María |last2=Martínez-Ballesteros |first2=María |last3=García-Gutiérrez |first3=Jorge |last4=Riquelme |first4=José C. |date=June 2019 |title=External clustering validity index based on chi-squared statistical test |url=https://linkinghub.elsevier.com/retrieve/pii/S0020025519301550 |journal=Information Sciences |language=en |volume=487 |pages=1–17 |doi=10.1016/j.ins.2019.02.046|hdl=11441/132081 |s2cid=93003939 |hdl-access=free }}</ref> is an external validation index that measure the clustering results by applying the [[Chi-squared test|chi-squared statistic]]. This index scores positively the fact that the labels are as sparse as possible across the clusters, i.e., that each cluster has as few different labels as possible. The higher the value of the Chi Index the greater the relationship between the resulting clusters and the label used.