1. Sampling

2. When we carry out research we need people to take part, these are called participants. It is important to use suitable participants in your study.
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3. The population is the group of people from whom the sample is drawn
The population is the group of people from whom the sample is drawn. For example if the sample of participants is taken from sixth form colleges in Leeds, the findings of the study can only be applied to that group of people and not all sixth form students in the UK and certainly not all people in the world.

4. Obviously it is not usually possible to test everyone in the target population so therefore psychologists use sampling techniques to choose people who are representative (typical) of the population as a whole. =
If your sample is representative then you can generalise the results of your study to the wider population.

5. Sampling Techniques
We will now examine some of the techniques used by Psychologists to obtain participants for their sample

6. Opportunity Sampling Common Room
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Want to be in my study?
Common Room
Opportunity sampling is the sampling technique most used by psychology students. It consists of taking the sample from people who are available at the time the study is carried out and fit the criteria you are looking for.

7. Random Sampling
This is a sampling technique which is defined as a sample in which every member of the population has an equal chance of being chosen. This involves identifying everyone in the target population and then selecting the number of participants you need in a way that gives everyone in the population an equal chance of being picked.

8. Stratified Sampling = 60% female 40% male = 60% female 40% male
Stratified sampling involves classifying the population into categories and then choosing a sample which consists of participants from each category in the same proportions as they are in the population.

9. Cluster Sampling Political group
This involves selecting a group (cluster) of individuals from a larger population. This may be less time consuming than random and more practical than inviting everyone in the phonebook. Cluster may be different from target population.

10. I know a lot about this problem, yes… Will you take part in my study
Purposive Sampling
I know a lot about this problem, yes…
Will you take part in my study
Individuals who are expected to provide the most appropriate information are invited to participate. The researchers opinions, prejudices are likely to create a bias sample. Rich data can be collected for qualitative research.

11. I’m in a study do you want to join? Yes and I’ll ask my friends to…
Snowball Sampling
I’m in a study do you want to join?
Yes and I’ll ask my friends to…
Participants ask each other or people they know to participate. This can obviously be biased but may be easier to gain a select group of participants eg investigating motivation and drug use.

12. In groups identify a strength and weakness of your sampling methods using p8-9
Bias – Non random and selected for a reason
Unrepresentative – Not typical of target population