This is one of the questions I’m asked most often. The answer is there is no “right” number. What I can say is that it depends on the nature of the role. First, it is important to describe that a competency model is designed to identify what is most critical to success in a role. If your model describes the technical and soft skills required to do that job, you want to be sure you cover it. But as you can imagine, there are probably a hundred soft skills that could be appropriate. So it’s important to pick the most important ones.
You also need to keep in mind the typical personality type of the person in that role. Sales people typically have a shorter attention span than technical people. So you’d want to have closer to 20 competencies in the Sales model and you could have 35 for a technical role.
When we create a custom competency model, we right-size the number by ensuring that we capture the key things that a person in the role does to be successful. And we generally use the soft skills to differentiate levels of proficiency. For example, instead of having 3 skills on analyzing and reporting out data, tailoring communication, and influencing, we have one skill on analyzing and reporting out data, where level 4 might be the ability to tailor communication to the needs of the individual and level 5 might be making a recommendation and influencing others to it. For more on how to do this, see the ATD webinar (http://webcasts.td.org/webinar/2235).