Sampling

Population: A group of people who are the focus of the researcher’s interest, from which a smaller sample is drawn.

Sample: A group of people who take part in a research investigation. This sample is drawn from a target population and is presumed to be representative of that population.

Sampling Techniques: The method used to select people from the population.

Bias: When certain groups are over or under-represented within the sample select which limits the extent to which generalisations can be made to the target population.

Generalisation: The extent to which findings and conclusions from a particular investigation can be broadly applied to the population. This is possible if the sample of participants is representative of the target population.

Random Sampling: A sample of participants produced by using a random technique such that every member of the target population being tested has an equal chance of being selected.

Random Sample Eval: Potentially unbiased however is difficult and time-consuming. The sample may still be unrepresentative and selected participants may refuse to take part.

Systematic Sample: A method of obtaining a representative sample by selecting every nth person. This can be random if the first person is selected using a random method; then you select every nth person after this.

Systematic Sample Eval: Objective sampling method so the researcher has no influence over who is chosen. However it’s time consuming and participants may refuse to take part.

Stratified Sampling: Groups of participants are selected in proportion to their frequency in the population in order to obtain a representative sample. The aim is to identify sections of the population, or strata, that need to be represented in the study. Individuals from those strata are then selected for the study using a random technique. If the sample is not randomly selected from the stratum, it is then a quota sample.

Stratified Sample Eval: Produces a representative sample of the population so generalisation of findings is possible however its time consuming and not always perfect.

Opportunity Sampling: A sample of participants produced by selecting people who are most easily available at the time of study.

Opportunity Sampling Eval: Its convenient and more economical. However it forms bias as the sample is unrepresentative of the target population as it drawn from a very specific area and the researcher has complete control over the selection of participants and may avoid those they don’t like the look of.

Volunteer Sampling: A sample of participants produced by a sampling technique that relies solely on inviting people to take part.

Volunteer Sampling Eval: Requires minimal input from the researcher and is less time-consuming. Volunteer bias occurs as a certain ‘type’ volunteers to partake and so may be more likely to try and please the researcher.