sampling

Population

A large group of individuals that a particular researcher is interested in studying from which a small sample is drawn.

Sample

A group of people who take part in a research investigation. The sample is drawn from the population and is supposed to be representative so that generalisation of findings becomes possible.

Sampling techniques

The method used to select people from the population this aims to produce a representative sample.

Random sample

Form of sampling in which all members of the target population have an equal chance of being selected. First you obtain a complete list of all members and secondly all of the names on the list are assigned a number. Finally, the actual sample is selected through the use of a lottery method.

Random sampling strengths

It is potentially unbiased and enhances internal validity

Random sampling limitations

It is difficult and time-consuming to conduct as it is extremely difficult to obtain members of the whole target population. May still end up with a sample that is unrepresentative. Selected participants may refuse to take part.

Systematic sampling

Where every nth member of a target population is selected. A list of people is organised and then nominated for example every third person.

Systematic sampling strength

It is objective and the researcher has no influence over who is chosen so there’s no bias involved

Systematic sampling limitation

It is time-consuming and participants may refuse to take part resulting in a volunteer sample

Stratified sample

This reflects the proportion of people in certain sub groups within the target population. Firstly you identify the different strata that make up the population then the proportions needed for the sample need to be representative or worked out. Finally, the participants that make up each Stratum are selected using random sampling.

Stratified sample strength

It is representative sample because it accurately reflects the composition of the population. This means that generalisation of findings becomes possible.

Stratified sampling limitations

Stratification is not perfect because the identified strata cannot reflect all the ways that people are different so complete representation of the target population is not possible.

Opportunity sample

As target populations are difficult to obtain researchers may simply decide to select anyone who happens to be willing and available.

Opportunities sampling strength

It is convenient and less costly as there is no need to divide the population into different group groups.

Opportunity sampling limitation

That can be two different forms of bias. The first is unrepresentative of the target population so the findings cannot be generalised. Second is the researcher has complete control over the selection of the participants leading to research a bias. This means they may avoid people they do not like the look of.

Volunteer sampling

Involves participants selecting themselves to be part of the sample which is referred to self selection

Volunteer sampling strengths

It is easy and requires minimal input from researcher so it is less time-consuming and the researcher end up with participants who are more engaged.

Volunteer sampling limitations

Volunteer bias. Asking for volunteers may attract a certain profile of people people who are curious and more likely to please the researcher. This affects how far findings can be generalised.