ANSWER
This question raises a common point of confusion for analysts and product managers as they identify and create personas.
Personas are used in User Centered Design to represent the audience that you are designing for. Each persona is a detailed profile of a fictional character which represents a different user segment. They are created in such a way as to bring a strong sense of realism to the users they represent. This helps create a visceral connection with the personas so that the system designer can really understand the users’ motivations for using the product. Personas primarily focus on a user’s attitudes and behaviors.
The analyst begins by documenting the motivators of behavior for the different types of potential system users. Information such as:
- Needs and Likes
- Dislikes
- Goals
- Beliefs
- Buyer personality type
- Available Free time
- Disposable income
- Demographic information that influences their use of the sytem.
This list is far from comprehensive and not all of these categories make sense for every situation. However, attention should be give to the final bullet point. At this step of the process you want to focus only on demographic data that specifically influences behavior (that is to say its a driver of the behavior). For instance, if my system is intended to sell school supplies then I likely want to document that the person is a parent. There is a direct cause and effect relationship between being a parent and purchasing school supplies. Other demographic information that doesn’t motivate or drive behavior isn’t needed at this time. In fact, by listing demographic data that doesn’t directly motivate a user the analyst can quickly lose focus of the primary goal of the exercise.
Next, by grouping together sets of common motivators and drivers that are present within various segments of the user base we identify our different personas.
If we determine that both men and women over 35 are just as likely to have the same drivers of behavior which lead them to purchase our product then for the sake of our persona we will simply pick a single gender. We pick a gender because we want our fictional character to seem as real as possible. So perhaps we make the persona female and call her Carrie.
Later in the exercise we can list other demographic segments that this one persona represents. I.e., we know it represents women over 35, but perhaps it also represents men over 35 because we decided these two groups would have the same motivation to purchase our product.
And this is ultimately the answer to our question. A persona is a very specific example of a demographic segment which focuses on the users motivations, behavior, and emotion. But personas can map to multiple demographic segments. So there is no need to create separate personas for each possible combination of demographic segment. Imagine how many personas you would need if you created a segment by the attributes Male/Female, Under 35/Over 35, Parent/Not Parent, Over $20k In Disposable Income/Under $20k, Homeowner/Renter, etc. Just with these demographic attributes alone we would have over 32 distinct combinations.
So in summary, focus on the motivators and drivers of behavior. Yes, some of these MIGHT be demographic attributes, but many demographic attributes are not drivers of behavior at all.
Here is a great real-life example of how User Personas are created and used.