Factor analysis
There are three major approaches to developing self-report inventories: theory-guided, factor analysis, and criterion-keyed. Theory-guided inventories are constructed around a theory of personality or a prototype of a construct. Factor analysis uses statistical methods to organize groups of related items into subscales. Criterion-keyed inventories include questions that have been shown to statistically discriminate between a comparison group and a criterion group, such as people with clinical diagnoses of depression versus a control group.