sampling

• population refers to the large group of individuals that a particular researcher may be interested in studying.
• Target population is too large to study, so the researcher selects a sample of this population.
• A sample is a group who take part in the researcher and is taken from the target population. Researchers aim to obtain a representative sample so that findings can be generalised.
• Bias


  bias can occur if certain groups may be over or under represented within the sample selected. This limits the extent to which generalisations can be made to the target population.
• generalisation

  extent to which the findings and conclusions from a study can be applied to the population. This is made possible if the sample of pps is representative of the population.
• opportunity sampling


  where a researcher decides to select anyone who is available and willing to participate n their study. Students are often in psychological research for this reason.
• strength of opportunity sampling

  method is convenient as it saves time, effort and is less costly.
• weakness of opportunity sampling

  likely to be unrepresentative of the target population as its dawn from a specific area e.g one street in one town.

  researcher has complete control over the selection of pps, they may simply avoid people they don't like the look of (researcher bias)
• random sampling

  form of sampling in which all members of the target population have an equal chance of being selected.
• random sampling

  to select a random sample a complete list of all members of the target population is obtained.

  all names are assigned a number.

  the sample is generated through the use of some lottery method (computer-based randomiser or picking numbers from a hat/container)
• random sampling strength

  free from researcher bias. researcher has no influence on who it is selected so selecting people who they think may support their hypothesis.
• random sampling weaknesses

  very difficult and time consuming to conduct. A complete list of the target population may be extremely difficult to obtain.

  pps selected may refuse to take part (resulting in further bias)
• systematic sample

  every nth member of the target population is selected .

  A sampling frame is produced, which is a list of people in the target population organised e.g alphabetical order.
• systematic sampling strengths

  avoids researcher bias. once the system for selection has been established the researcher has no influence over who is chosen.

  usually fairly representative.
• systematic sampling weakness

  process of selection can interact with hidden traits within the population. If the sampling technique coincides with the frequency of the trait, the sampling technique is neither random or representative. #
• stratified sampling

  a sub-group is created of the wider population based on age, social class etc. then the population is randomly sampled within each stata
• stratified sampling

  to carry stratified sample the researcher first identifies the different strata that makes up the population.

  The proportions needed for the sample to be representative are worked out.

  the pps that make up each strata are selected randomly.
• strength of stratified sampling

  avoids researcher bias, the target population has been sub-divided into strata, the pps that make up the numbers are randomly selected.

  method produces a representative sample as its designed to accurately reflect the population, meaning generalisation of findingd becomes possible.
• weaknesses of stratified sampling

  requires a detailed knowledge of the population characteristics, which may not be available.

  very time consuming, dividing a sample into strata and then randomly selecting from each.
• volunteering sampling


  pps select themselves to be a part of the study.

  researcher may place an advert online, newspaper, noticeboard and people respond wanting to take part in the study.
• strength of volunteering sampling

  sample requires little effort from researcher as pps volunteer themselves.
• weaknesses volunteering sampling

  sample will be bias and unrepresentative as volunteers tend to be a certain 'type' of person. This makes results difficult to generalise to a target population.

  volunteers are eager to please, which increases the chances of demand characteristics e.g giving the answer they think is required.