What are the various methods used to perform Job Analysis?

1. Observation: This was the first method of job analysis used by I-O psychologists. The process involves simply watching incumbents perform their jobs and taking notes. Sometimes they ask questions while watching, and commonly they even perform job tasks themselves. Near the end of World War II, Morris Viteles studied the job of navigator on a submarine. He attempted to steer the submarine toward Bermuda. After multiple misses by over100 miles in one direction or another, one officer suggested that Viteles raise the periscope, look for clouds, and steer toward them since clouds tend to form above or near land masses. The vessel reached Bermuda shortly after that suggestion. The more jobs one seriously observes, the better one's understanding becomes of both the jobs in question and work in general.
2. Interviews: It is essential to supplement observation by talking with incumbents. These interviews are most effective when structured with a specific set of questions based on observations, other analyses of the types of jobs in question, or prior discussions with human resources representatives, trainers, or managers knowledgeable about jobs.
3. Critical incidents and work diaries: The critical incident technique asks subject matter experts to identify critical aspects of behavior or performance in a particular job that led to success or failure. For example, the supervisor of an electric utility repairman might report that in a very time-pressing project, the repairman failed to check a blueprint and as a result cut a line, causing a massive power loss. In fact, this is what happened in Los Angeles in September2005 when half the city lost power over a period of12 hours. The second method, a work diary, asks workers and/or supervisors to keep a log of activities over a prescribed period of time. They may be asked to simply write down what they were doing at15 minutes after the hour for each hour of the work day. Or, they may list everything they have done up to a break.
4. Questionnaires and surveys: Expert incumbents or supervisors often respond to questionnaires or surveys as a part of job analysis. These questionnaires include task statements in the form of worker behaviors. Subject matter experts are asked to rate each statement form their experience on a number of different dimensions like importance to overall job success, frequency performance and whether the task must be performed on the first day of work or can be learned gradually on the job. Questionnaires also ask incumbents to rate the importance of KSAOs for performing tasks, and may ask the subject matter experts to rate work context. Unlike the results of observations and interviews, the questionnaire responses can be statistically analyzed to provide a more objective record of the components of the job. To a greater and greater extent, these questionnaires and surveys are being administered online to incumbents.
5. Position Analysis Questionnaire: The Position Analysis Questionnaire (PAQ) is a well-known job analysis instrument. Although it is labeled a questionnaire, the PAQ is actually designed to be completed by a trained job analyst who interviews the SMEs (e.g., job incumbents and their supervisors).[2] The PAQ was designed to measure job component validity of attributes presented in aptitude tests. Job component validity is the relationship between test scores and skills required for good job performance. There are195 behavior-related statements in the PAQ divided into six major sections: information input, mental process, work output, relationships with others, job context, and other job characteristics.
6. Checklists: Checklists are also used as a job analysis method, specifically with areas like the Air Force. In the checklist method, the incumbent checks the tasks he or she performs from a list of task statements that describe the job. The checklist is preceded by some sort of job analysis and is usually followed by the development of work activity compilations or job descriptions. The scope of task statements listed depends upon the judgment of the checklist constructor.

well Common methods of job analysis include the following

1. observation method.

2. checklist method.

3. structural questionnaire method.

1. Technical conference method.

2. Diary method.

3. Observation method.

4. Individual interview.

5. Group interview.

6. Structure questionnaire method.

the basic answer for job analysis

1 performance is the best way of job analysis.

I believe they are :

1.Observation method.

2.Work sampling method.

3.Employee diary or work log method.

4.Interviewing method.

5.Questionnaires  method.

1. Trained Job Analysts

2. Supervisors

3. Incumbents

4. Observation

5. Individual Interviews (with job incumbents)

6. Group Interviews

7. Questionnaires (either structured or open-ended)

8. Work Diarys

9. Critical Incidents

10. Recording of Job Activities

The purpose of job analysis is to combine the task demands of a job with our knowledge of human attributes and produce a theory of behaviour for the job in question. There are two ways to approach building that theory, meaning there are two different approaches to job analysis.

Task-oriented

Task-oriented procedures focus on the actual activities involved in performing work.This procedure takes into consideration work duties, responsibilities, and functions. The job analyst then develops task statements which clearly state the tasks that are performed with great detail. After creating task statements, job analysts rate the tasks on scales indicating importance, difficulty, frequency, and consequences of error. Based on these ratings, a greater sense of understanding of a job can be attained. Task analysis, such as cognitively oriented task analysis (COTA), are techniques used to describe job expertise. For example, the job analysts may tour the job site and observe workers performing their jobs. During the tour the analyst may collect materials that directly or indirectly indicate required skills (duty statements, instructions, safety manuals, quality charts, etc.).

Functional job analysis (FJA) is a classic example of a task-oriented technique. Developed by Fine and Cronshaw in1944, work elements are scored in terms of relatedness to data (0–6), people (0–8), and things (0–6), with lower scores representing greater complexity. Incumbents, considered subject matter experts (SMEs), are relied upon, usually in a panel, to report elements of their work to the job analyst. Using incumbent reports, the analyst uses Fine's terminology to compile statements reflecting the work being performed in terms of data, people, and things. The Dictionary of Occupational Titles uses elements of the FJA in defining jobs.

Worker-oriented

Worker-oriented procedures aim to examine the human attributes needed to perform the job successfully.[8] These human attributes have been commonly classified into four categories: knowledge, skills, abilities, and other characteristics (KSAO). Knowledge is the information people need in order to perform the job. Skills are the proficiencies needed to perform each task. Abilities are the attributes that are relatively stable over time. Other characteristics are all other attributes, usually personality factors. The KSAOs required for a job are inferred from the most frequently-occurring, important tasks. In a worker-oriented job analysis, the skills are inferred from tasks and the skills are rated directly in terms of importance of frequency. This often results in data that immediately imply the important KSAOs. However, it can be hard for SMEs to rate skills directly.

The Fleishman Job Analysis System (F-JAS) developed by Edwin A. Fleishman represents a worker-oriented approach. Fleishman factor-analyzed large data sets to discover a common, minimum set of KSAOs across different jobs. His system of73 specific scales measure three broad areas: Cognitive (Verbal Abilities; Idea Generation & Reasoning Abilities; Quantitative Abilities; Memory; Perceptual Abilities; Spatial Abilities; and Attentiveness), Psychomotor (Fine Manipulative Abilities; Control Movement Abilities; and Reaction Time and Speed Abilities), and Physical (Physical Strength Abilities; Endurance; Flexibility, Balance, and Coordination; Visual Abilities; and Auditory and Speech Abilities).

JobScan is a measurement instrument which defines the personality dynamics within a specific type of job. By collecting PDP ProScan Survey results of actual performers and results of job dynamics analysis surveys completed by knowledgeable people related to a specific job, JobScan provides a suggested ideal job model for that position. Although it does not evaluate the intellect or experience necessary to accomplish a task, it does deal with the personality of the type of work itself.

All answered very well, I think I am very late.  Thanks for all colleagues  for their excellent answers.