Sampling-research methods

Sampling

• .Testing part of the population.
• .Ideally a sample is representative.
• .Target population-indicates the group of people that the results are targeted at.

Random sampling

• .Each member of a population has an equal chance of being selected.
• .All names from target population could be placed in a container and the required sample number could be drawn out OR computer programs also used to generate random lists.
• Strengths :
• -Unbiased selection-
• -Generalisation (to the target population)
• Weaknesses:
• -Impractical-difficult to get details of the whole population and not all members may be available or wish to take part.
• -Not representative-unbiased selection does not guarantee an unbiased sample, therefor results are not necessarily generalisable.

Opportunity sampling

• .Involves selecting participants who are available and willing to take part.
• Strengths:
• .Ease of formation- they use people who are readily available.
• .Natural experiments- with natural experiments opportunity sampling must be used as the researcher has no control over who is being studied.
• Weaknesses:
• .Unrepresentative-The sample is likely to be biased by excluding certain types of participants, so findings can't be generalised to the target population.
• .Self selection-participants have the option to decline or take part.

Volunteer (self-selected) sampling

• .People volunteer to participate (often replying to adverts).
• Strengths:
• .Ease of formation-requires little effort from researcher.
• .Less chance of 'score you' phenomenon- As participants are eager to take part there will be less chance of them deliberately trying to sabotage the study.
• Weaknesses:
• .Unrepresentative-The sample will be biased, volunteers tend to be a certain 'type' of person, therefore results aren't generalisable to target population.
• .Demand Characteristics-volunteers are eager to please, which increases the chances of demand characteristics.

Systematic sampling

• .Involves taking every nth person from a list to create a sample.
• Strengths-
• .Unbiased selection- increased chances or a representative sample.
• .Generalisation-The results are likely to be representative.
• Weaknesses:
• .Periodic traits- The process of selection can interact with a hidden periodic trait within the population.
• .Not representative- Unbiased selection does not guarantee an unbiased sample.

Stratified sampling

• .A small scale reproduction of the population.
• .It involves dividing a population into characteristics important for the research (e.g. age,social class), then the population is randomly sampled within each stratum (category).
• Strengths:
• .Representative-A selection occurs from representative sub-groups within a population.
• .Unbiased-random sampling is performed on sub-groups of the population.
• Weaknesses:
• .Knowledge of population characteristics is required-detailed knowledge is required which may not be available.
• .Time consuming