Random samples require a way of naming or numbering the target population and then using some type of raffle method to choose those to make up the sample. If the “population” is everyone who has bought a lottery ticket, then each person has an equal chance of winning the lottery (assuming they all have one ticket each). Random sampling is a type of probability sampling where everyone in the entire target population has an equal chance of being selected. The one chosen will depend on a number of factors (such as time, money etc.). But who are you going to try it out on and how will you select your participants? OK, so you’ve thought up this brilliant psychological study and designed it perfectly. Many psychology studies have a biased sample because they have used an opportunity sample that comprises university students as their participants (e.g. Sampling bias refers to situations where the sample does not reflect the characteristics of the target population. One of the problems that can occur when selecting a sample from a target population is sampling bias. The more representative the sample, the more confident the researcher can be that the results can be generalized to the target population.

This is important because we want to generalize from the sample to target population. It is more or less impossible to study every single person in a target population so psychologists select a sample or sub-group of the population that is likely to be representative of the target population we are interested in. In some types of research the target population might be as broad as all humans, but in other types of research the target population might be a smaller group such as teenagers, pre-school children or people who misuse drugs. We call the group that we are interested in studying our 'target population'. In psychological research we are interested in learning about large groups of people who all have something in common.

This limits how much the findings of the study can be generalised to the whole population.

For instance if only males are selected, or if the advert for volunteers is put into the Guardian, only people who read the Guardian are selected.

Biased sample iswWhen certain groups are over or under represented within the sample selected.

This can only occur if the sample of participants is representative of the population.

Generalisability refers to the extent to which we can apply the findings of our research to the target population we are interested in.

The people who take part are referred to as “participants”.

A sample is the group of people who take part in the investigation.

The target population is the total group of individuals from which the sample might be drawn.

Sampling is the process of selecting a representative group from the population under study.

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