The method of specifically identifying clusters of related items on a test that measure a common ability is called

Factor analysis.

Explanation:

The key concept of this analysis method is seen that a lot of variables which are seen to have like terms and also variables are seen to worked on severally to produce the given output/result. It is known to be not a singular pattern but it is seen to have a family group pattern because of its involvement with multiple variables.  

It is also widely used in thesis researches and also dissertation like sometimes seen to be used in developing tests for psychological measurements etc.

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