SJT's measure procedural knowledge; the knowledge about the performing of tasks that is often job related. Research on SJT's show there is a relation between SJT's, personality, cognitive ability and experience. SJT's offer incremental validity as well. This means that SJT's uniquely add to the prediction of job performance. The relation between these different elements is best described by the following diagram:
Implicit trait policies: or ITP's, are implicit beliefs about the relationship between expression of certain personality traits and effectiveness in different (job related) situations. If the ITP's of a person are correct, they will be able to show the desired behavior at the right time. As can be seen from the diagram, these trait policies originate from general experience. A person experiences different situations and consequences in their life time, resulting in their own understanding of 'cause and effect'. Their personality dictates what situations they experience more often or what type of reaction they are prone to give resulting in general domain knowledge.
Specific Job Knowledge: specific job knowledge is the knowledge about effective action that may be unique to a specific job or job group. This type of knowledge can only be learned by experiencing the job itself.
Both ITP's and Specific Job knowledge have an independent effect on job performance. Accurate ITP's can compensate for lack of job knowledge and specific job knowledge can compensate for inaccurate ITP's. A person can already have some related ITP's causing the job specific knowledge to be easily learned.