Title: Non-probability samples
Course: UGQuants (SSPS) > Section: Survey Design

Non-probability samples

The reality of both the research process and the social world often means there are situations where probability sampling is either unfeasible or unnecessary. In such situations, we can use non-probability sampling techniques. As noted previously, 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. Despite having a number of limitations which we will consider, the non-probability sample can be the appropriate technique to use in certain research situations. Firstly, where a sampling frame is unavailable, probability sampling will not be possible. Secondly, where a researcher is carrying out a qualitative study, a pilot study or an exploratory study, probability sampling is not usually necessary. Finally, there can be situations where the research does not seek to produce generalisable results and the use of a non-probability sample will again be appropriate.

Whilst non-probability sampling can be an appropriate technique in a number of circumstances, its key disadvantage must always be kept in mind: that is that an unknown proportion of the population of interest is not sampled.

There are several types of non-probability samples which we will now consider: convenience sampling, purposive sampling and quota sampling.