Unit 2 - Participants (sampling)

What must psychologists ensure when selecting their sample?

That it is representative of the sub-groups within the target population as this will impact the validity of their results. If the sample is representative, the results can be generalised to the target population, but if it is not representative, it may be considered invalid or lacking population validity.

How must psychologists select participants?

In an unbiased way to be fair and appropriate to members of the target population, but it must not be too costly or time consuming.

What is ‘random sampling’?

Where participants are selected from the sampling frame, and everyone has an equal chance of being selected. This could be done by lottery, random number generator, a spreadsheet or more. One strength of this is that it’s a fair method as everyone in the target population has an equal chance of being selected, but a weakness is that the sample may be biased and not representative.

What is ‘opportunity sampling’?

Where participants are selected at the researcher’s convenience without knowing any details about the sample in advance. A strength is that it is way easier to recruit participants in comparison to other techniques which may be more costly, yet a weakness is that you may end up with a biased sample based on who was available at the time, and there may also be some researcher bias when selecting participants.

What is ‘systematic sampling’?

where every nth person on a list is selected by the researcher. A strength is that as long as the first participant is selected randomly, there can be no researcher bias, however, a weakness is that you may still end up with a biased sample.

What is ‘stratified sampling’?

Where the target population is divided into subgroups and then the participants are selected randomly from each subgroup. A strength is that it is guaranteed that all subgroups in the target population will be represented in the sample, but a weakness is that it is more difficult for the researcher to complete compared to other sampling methods.

What is ‘quota sampling’?

where the target population is divided into subgroups and that participants are chosen from each subgroup at the convenience of the researcher. A strength is that we can guarantee that all subgroups in the target population will be represented in the sample, however, a weakness is that it is more difficult for a researcher to complete than other sampling techniques.

What is ‘self-selected/volunteer sampling’?

Where participants volunteer for researcher after reading an advertisement. A strength is that participants are interested in taking part, but a weakness is that volunteers may not be from appropriate subgroups within the target population.

What is ‘snowball sampling’?

Where participants are initially recruited by researchers and then those participants are further recruited from people they know. A strength is that it is a helpful technique for investigating rare characteristics or behaviours, but a weakness is that the initial participants may not know sufficient participants who share their characteristic.