Determining the competencies that are needed to be successful in a given job, or group of similar jobs, is the first step to improving the hiring or selection processes, determining training needs, building effective feedback systems, or creating career development programs.
There are numerous ways of determining competencies, some more time consuming and expensive than others. Careful consideration needs to be given to the ultimate use for the results when selecting the method. For example, if the sole desire to develop training for a group of staff, assembling a focus group and working through a collaborative process will probably suffice; a few hours and you are done.
However, if the intent is to ultimately use the results for other purposes, selection for example, then a more systematic and legally defensible process is probably needed. Job task information should be solicited, criticality and frequency ratings collected, and the resulting data used to determine critical job tasks and the competencies needed to perform those tasks.
Regardless of the ultimate use, it should not be a time consuming and expensive process. A few days of labor (at the most) should produce quality results, well defined competencies, and the supporting data to document the process.
It is important to spend to time needed to get accurate data upon which to determine needed competencies. After all, everything else is built on this foundation; you want it to be solid.