The content model is intended to be a taxonomy of occupational descriptors. An important first step in developing a taxonomy is to define the unit of analysis. In O*NET, this is the occupation, rather than the job or position. An occupation is broader than a specific job or specific position, and it is not idiosyncratic to a particular organization, industry, or setting. A particular occupation could include several jobs if the general responsibilities, activities, and requirements for the various jobs are substantially similar. For example, the occupation “commercial aircraft pilot” could include many different jobs as a function of type of organization, type of aircraft, and business function (see Chapter 3 for further discussion).

With occupations as the unit of analysis and the characteristics of these occupations, such as the physical and cognitive abilities they require of workers, to be included in a taxonomy of descriptors, a number of other important questions become relevant:

  1. How general or specific will the descriptors of occupational requirements be? For example, when considering how to develop a taxonomy of the abilities required by occupations, previous research provides taxonomies that define abilities in terms of two groups of factors (clusters of more specific abilities), four groups of factors, eight groups of factors, or some greater number (see Carroll, 1993).

  2. Given a particular level of generality/specificity, should the set of descriptors of a particular occupational requirement (e.g., knowledge, ability) be a representative sample of all possible descriptors of that requirement, or should it represent the entire universe of descriptors? Previous research-based taxonomies of human abilities (Carroll, 1993) are meant to describe the full range of human abilities, rather than a representative sample. Is this exhaustive approach to be applied when developing descriptors for all of the occupational requirements?

  3. Should each descriptor of occupational requirements be applicable to every occupation (i.e., unit of analysis)? To return to the example of abilities, previous taxonomies have been designed to include descriptors that can be measured across all individuals. They do not include any descriptors of abilities that are applicable only to men or only to women.

  4. Is the taxonomy to include genuine taxons, such as those in biology? In biology, a taxon is defined as a group of organisms with common characteristics, in varying degrees of distinction, such as a phylum, order, family, genus, or species. Common physical

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