Since these researchers are measuring suicidal potential rather than ideation the questions are broad based and include social factors such as school and home life. They carefully tested the validity of the questions, internal consistency and test-retest reliability. Test-retest reliability is an important factor in determining if a self-reporting instrument is valid over time. the CASPI had a .76 score which the authors report is consistent with other testing instruments. The retest was conducted two weeks after the initial screening, which could be a factor in its high reliability score. The CASPI instrument was measured against known suicidal potential in the population sampled in order to assess its true validity.
It appears that the researchers were successful in formulating questions with enough neutrality that children and adolescents could answer them honestly. The subpopulation of young children (less than 13 years old) is notoriously hard to assess, but this instrument appears to be consistent and valid even with younger children. It was more consistent and valid with older children, however (up to 96 percent accurate in distinguishing levels of suicidal potential). This instrument was tested with a significant number of students with a diverse cross section of socio-economic circumstances and ethnicities. This is a key element which is sometimes lacking in validating other self-reporting instruments. It also asks questions about family history, which is an important indicator of suicidal potentiality that is sometimes left out of other reporting instruments.
Self-reporting instruments are as accurate as the people taking them—if the participant completes them honestly, they will measure suicidal potential. Self-reporting instruments require an ability to self-reflect as well as a willingness to open up through the anonymity of a questionnaire.