At its most basic, the term “population” simply means a group of people, defined according to specific characteristics. For instance, we might describe all of the people living in Canada as the Canadian population, in which case, geography and/or political boundaries would be the defining characteristic of the population. Geography almost always plays a part in describing a population, but other characteristics can also be used to refine our description or focus. When we collect information about females and males living in Nova Scotia, for example, we are still using a geographic definition of population – the province – but we are asking how sex affects the needs and experiences of that population. Many other characteristics can be used to describe populations: age, rural living, education, home-ownership, sexual orientation, ability, etc. When we focus on the needs or experiences of a specific part of the population, such as Aboriginal youth in Manitoba or female tobacco users in British Columbia, we sometimes refer to this group as a “sub-population”.
While a population may be identified by specific characteristics, such as sex or ethnicity, it can also be defined by relationships and shared interests. For example, when a group of practitioners with particular skills and knowledge come together to share their experiences and insights, we refer to them as a “community of practice”. An association of midwives who meet to talk about their practical experiences with homebirth would be an example of a community of practice. Individuals within this group may come from different places and different backgrounds, but they form a population through their relationships with one another.
A “community of interest” may also constitute a population. In this case, a group of people come together to share information and opinions about a particular topic of concern to them. A group of parents who meet to discuss neighbourhood playground health and safety would be a community of interest. Communities of interest differ from communities of practice in that particular expertise is not required. Members of the group simply have to have an interest and be willing to exchange information, ask questions, and express their views.
As we work at defining a population, it is important to remember that learning about a group of people does not mean that we will automatically understand the needs of every individual within that group. For example, much attention is currently being paid to Canada’s aging population and the demands it will place on the health care system and other social programs. Although many people over the age of 65 do have increased health care needs, many do not. Planning for a greater investment in health care for seniors may be sensible for the population as a whole without being necessary for individual seniors. This tension between the needs of a population and the needs of an individual is ever present in research as well as in health policy and planning.
Identifying a population is a challenging task. For various reasons, including resources, availability of information, and complexity of analysis, we cannot include every characteristic or every group in our definitions. But the choice of which characteristics to include and which groups to focus on has consequences for how we understand and respond to the needs of populations.