Guidelines for Essential Versus Marginal Functions
The Americans With Disabilities Act (ADA) requires employers to make job-related decisions on the basis of whether a person can perform essential job functions, under reasonably accommodating conditions, in an acceptable manner. Job descriptions must identify which functions are essential, and employers must make employment decisions based upon the essential functions. Other functions, not designated essential, are categorized as marginal and are not to be used as a basis for employment decisions. Both essential and marginal functions must be identified in job descriptions.
An essential function is a duty or responsibility that is fundamental to the job -- a critical, or basic component of that job. A marginal function is relatively incidental to the reason for the job's existence. An essential function can not or should not be assigned elsewhere, but a marginal function, even though it is desirable to include in the job design, could be made part of another job without causing significant problems.
A marginal function is not unessential to the work unit, only to a given job. The function has to be accomplished, but it can be done by another employee or position.
An article by P.C. Grant in Business Horizons (1997, March-April), "Essential or marginal? Job functions and the Americans with Disabilities Act," provides the following guidance.
Three factors to consider when evaluating a function as essential or marginal:
Relationship of the functions to other tasks within the job
How reassigning the functions will affect other employees and their jobs
Significance of the function and the conditions under which it is performed
For example, a job requires the operation of a machine. In the job description, “painting the machine twice a month” is stated. However, this is not critical to the execution of the job. “Operating the machine” is the critical role, hence it is listed in the “essential functions”. “Painting the machine” is not critical to the performance; hence, it is listed in the “marginal functions”. Redistributing the “painting the machine” function would not alter the “Machine Operators” job description.