On one hand, some theorists and practicioners incorporate job analysis and competency modeling into a functional pair when discussing or performing job assessments for a business or corporation. On the other hand, some theorists state that job analysis is redundant of the more contemporary competency modeling and is therefore out-moded or even "dead."
In the first case (functional pair), job analysis is seen as the information gathering phase of job assessment during which either (1) worker/person-oriented job analysis or (2) work/task-oriented job analysis is undertaken to determine (1a) the personal attributes needed to complete the job (often called job specifications), e.g., motives, personality, values, interests, or to determine (2a) what gets done (e.g., packing cans; keeping accounts) and how the job is done (e.g., machinery, forklift; analyze data, graphs showing data analysis) (often called job description). Competency modeling is different from job analysis because it follows job analysis and uses the data gathered during job analysis. Competency modeling structures whole oragnaizations or departments or job-type groups according to the results of the job analysis and according to the knowledge, skills, abilities or other personality traits (KSAOs) needed by the worker/person-orientation or the work/task-orientation to fulfill the job or role or function required.
In this perspective, job analysis is different from competency modeling in that it produces fact gathering, generates fact analysis and is more individually rather than corporately oriented. In this perspective, competency modeling is different from job analysis in that it applies the data gathered and analyzed to a model of operation that can be applied at whichever business or corporate level it is needed, and it has a holistic orientation rather than an individual orientation (competency modeling can be utilized for a bottom-up competency model focusing on individual jobs or in a top-down, compartmentalized competency model focusing on the whole corporation or on corporate levels).
In the second case (redundant concepts), competency modeling is essentially similar to job analysis. Both analyze job needs based on person performing the job and on tools/skills used in performing the job. Still, there is a difference between the two in that competency modeling allows readily for a holistic view (whole corporation, whole department, whole job category) while job analysis is particularly oriented to an individualistic view of jobs and job performance. They are similar, however in that both depend upon KSAOs while performing analysis or modeling.
The major similarity between these two is that they both have the same purpose. Both are meant to identify the requirements for performing a given task. Both can be used to figure out what sort of person (or what specific person) should be selected for a given job.
The major difference is that job analysis looks at the details of the job while the competency model looks at the attributes of the person. In the job analysis model, extensive data is gathered about what a particular job actually entails. It is then important to go out and find a person who can do those things (or can be trained to do them). By contrast, the competency model focuses on "KSAOs." That stands for "Knowledge," "Skills," "Abilities," and "Other individual characteristics. Such an analysis tries to determine what KSAOs are needed in order to excel at a given job. It focuses on the person rather than on the task.
Both approaches can be useful and both have the same goal, but they go about reaching that goal in very different ways.