It is easy to assemble a set of user characteristics and call it a persona, but it's not so easy to create personas that are truly effective tools for innovation, design, and communication. A good persona description is not a list of tasks or duties; it's a narrative that illuminates their skills, attitudes, environment, goals, and needs and desires.

Personas are synthesized from in-depth engagements with a relatively small number of real people that represent the larger community, and captured in a structured definition that includes behavior patterns, goals, skills, attitudes, and needs and desires. They may include a few reality-based personal details to bring the persona to life. Personas are always created within a context that defines the ‘environment of interest’. For example, a context may be something like ‘perceptions of vehicle safety’ or ‘drug therapy compliance’. This defines the focus of the specific in-depth engagements and, hence, the discovered behaviors, goals, and needs and desires of the personas being developed. There is no ‘global’ set of personas (like Meyers-Briggs is for personality traits) that can be used for all research efforts. Like traditional market segmentation, the more focused the context, the more accurate the personas. Personas are specific to a particular innovation, design, or communication effort.

For each context, there is a small set of personas, usually from 4 to 10, that adequately represents the universe of people of interest. Ideally, you should seek the minimum number of personas required to illustrate key goals and behavior patterns. There's no magic number, but if you're designing a product and you have a dozen personas, then you may be making distinctions that are not very important.