We've been designing compensation programs and processes, each requiring writing job descriptions, for almost 25 years. Not once in all that time have I ever found a compensation analyst or anyone else for that matter, who likes to write job descriptions or go through the process leading up to their writing. To put it mildly, anything to do with such descriptions can only be described as tedium. And that's too bad because the job description is such an important and useful tool. Before we can discuss job descriptions, it is important to understand the distinction between descriptions and specifications.
Job analysis is the combination of job descriptions and job specifications.
However, three years' experience in the particular position may indeed be necessary. Each responsibility should start with a verb which describes the activity. There are hundred of such verbs and by using such terms that most people understand, one minimizes the chances that the responsibilities will be misinterpreted or misunderstood. Usually, especially for exempt positions, information about a position is obtained by interviewing the incumbent. For nonexempt positions, interviewing might take place, but usually the information is obtained through the use of a questionnaire.