As you continue planning your research project you need to think about how you’re going to choose your participants. By now you should have decided what type of people you need to contact. For some research projects, there will be only a small number of people within your research population, in which case it might be possible to contact everyone. This is called a census. However, for most projects, unless you have a huge budget, limitless timescale and large team of interviewers, it will be difficult to speak to every person within your research population.

SAMPLING

Researchers overcome this problem by choosing a smaller, more manageable number of people to take part in their research. This is called sampling. In quantitative research, it is believed that if this sample is chosen carefully using the correct procedure, it is then possible to generalise the results to the whole of the research population. For many qualitative researchers however, the ability to generalise their work to the whole research population is not the goal. Instead, they might seek to describe or explain what is happening within a smaller group of people. This, they believe, might provide insights into the behaviour of the wider research population, but they accept that everyone is different and that if the research were to be conducted with another group of people the results might not be the same.

Sampling procedures are used everyday. Market researchers use them to find out what the general population think about a new product or new advertisement. When they report that 87% of the population like the smell of a new brand of washing powder, they haven’t spoken to the whole population, but instead have contacted only a sample of people which they believe are able to represent the whole population. When we hear that 42% of the population intend to vote Labour at the next General Election, only a sample of people have been asked about their voting intentions. If the sample has not been chosen very carefully, the results of such surveys can be misleading. Imagine how misleading the results of a ‘national’ survey on voting habits would be if the interviews were conducted only in the leafy suburbs of an English southern city. Probability samples and purposive samples There are many different ways to choose a sample, and the method used will depend upon the area of research, research methodology and preference of the researcher. Basically there are two main types of sample:

1. probability samples
2. purposive samples

In probability samples, all people within the research population have a specifiable chance of being selected. These types of sample are used if the researcher wishes to explain, predict or generalise to the whole research population.

On the other hand, purposive samples are used if description rather than generalisation is the goal. In this type of sample it is not possible to specify the possibility of one person being included in the sample. Within the probability and purposive categories there are several different sampling methods.

The best way to illustrate these sampling methods is to take one issue and show how the focus of the research and the methodology leads to the use of different sampling methods. The area of research is ‘school detention’ and in Table 3 you can see that the focus and sampling techniques within this topic can be very different, depending on the preferences of the researcher, the purpose of the research and the available resources.

SAMPLE SIZE

The first question new researchers tend to ask is ‘how many people should I speak to?’ This obviously depends on the type of research. For large scale, quantitative surveys you will need to contact many more people than you would for a small, qualitative piece of research. The sample size will also depend on what you want to do with your results. If you intend to produce large amounts of cross tabulations, the more people you contact the better. It tends to be a general rule in quantitative research that the larger the sample the more accurate your results.

However, you have to remember that you are probably restricted by time and money – you have to make sure that you construct a sample which will be manageable. Also, you have to account for non-response and you may need to choose a higher proportion of your research population as your sample to overcome this problem. If you’re interested in large-scale quantitative research, statistical methods can be used to choose the size of sample required for a given level of accuracy and the ability to make generalisations. If your research requires the use of purposive sampling techniques, it may be difficult to specify at the beginning of your research how many people you intend to contact. Instead you continue using your chosen procedure such as snowballing or theoretical sampling until a ‘saturation point’ is reached. This was a term used by Glaser and Strauss (1967) to describe that time of your research when you really do think that everything is complete and that you’re not obtaining any new information by continuing. In your written report you can then describe your sampling procedure, including a description of how many people were contacted.

SUMMARY

•  If it is not possible to contact everyone in the research population, researchers select a number of people to contact. This is called sampling.   There are two main types of sampling category – probability samples and purposive samples.
•  In probability samples, all people within the research population have a specifiable chance of being selected.
• Only within random samples do participants have an equal chance of being selected.
•  Purposive samples are used if generalisation is not the goal.
•  The size of sample will depend upon the type and purpose of the research.
•  Sample sizes should take into account issues of non-response.
•  Remember that with postal surveys it might be difficult to control and know who has filled in a questionnaire. Will this affect your sample?
•  In some purposive samples it is difficult to specify at the beginning of the research how many people will be contacted.
•  It is possible to use a mixture of sampling techniques within one project which may help to overcome some of the disadvantages found within different procedures.