This sampling method is not a fixed or pre-defined selection process which makes it difficult for all elements of a population to have equal opportunities to be included in a sample. Disadvantages include an increased risk of bias, if the chosen clusters are not representative of the population, resulting in an increased sampling error.
However, by selecting friends and acquaintances of subjects already investigated, there is a significant risk of selection bias choosing a large number of people with similar characteristics or views to the initial individual identified.
For example, it will be extremely challenging to survey shelterless people or illegal immigrants.
This is a quick way and easy of choosing participants advantagebut may not provide a representative sample, and could be biased disadvantage.
Random Sampling Random sampling is a type of probability sampling where everyone in the entire target population has an equal chance of being selected.
This method is rarely used in Psychology. For instance, it is easier to contact lots of individuals in a few GP practices than a few individuals in many different GP practices. This may involve specifically targeting hard to reach groups. All members of the selected households clusters are included in the survey.
It gets rid of bias in the population and gives a fair chance to all members to be included in the sample. The selection of the sample largely depicts the understanding and the inference of the researcher.
Difference between Probability Sampling and Non-Probability Sampling Methods We have looked at the different types of sampling methods above and their subtypes.