Sampling 1

A population is a group that we want to find information about. It might be a group of people or it could be simply a group of numbers.

A census is when information about every member of the population is collected. The disadvantage of this method is that if the population is large, it can be difficult to collect and process so much information.

A sample survey is when information is collected from a small representation of the population. For example, if we were trying to find out what Britain's favourite TV show is, it would be impractical to ask everybody in the country (as a census would do). Instead, 1000 people might be chosen and asked.

A sampling unit is a person/object to be sampled. The sampling units must be defined in such a way that any one member of a population is not sampled more than once. For example, if we were trying to find out how many cars the average family owns, the sampling unit would be a household rather than an individual, because we wouldn't want to ask two people from the same household.

A sampling frame is the collection of all of the sampling units. Ideally, this should cover the whole population.