Title: 2. What or who to survey?
Course: UGQuants (SSPS) > Section: Survey Design

What/who to survey?

Once we have decided upon the phenomenon that we wish to investigate, we need to think about what/who we want to survey. In some cases we may want to survey the entire population of interest. This is known as a census and is obtained by gathering information about every member of the population of interest. It is important to note that in survey research, the term population does not necessarily refer to the population of a country or a specific region but instead refers to the set of units the sample is meant to represent. The units which make up the population will depend on the units of analysis and need not necessarily be people. For example, the population units could be nations, cities, regions or companies.

In many circumstances, it will simply not be feasible to survey the entire population, and we must therefore select a sample. A sample is a subset of the population of interest and is obtained by collecting information about only some members of the population. In order to do this, we must define the population of interest before obtaining a sampling frame (a list of all members of the population from which our sample will be chosen) from which we then select our sample.

Broadly speaking, there are two types of samples, namely probability and non-probability. In short, a probability sample is a sample which has been selected using a method of random selection so that each member of the population has an equal chance of being selected. Conversely, a non-probability sample is a sample that has not been selected using a method of random selection meaning that some members of the population have a greater chance of being selected than others. We will now consider both types of sample.