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Sampling

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Sampling

  1. 1. Research Methods
  2. 2. • Define the following terms • population • sample • representative sample
  3. 3. Participant selection and allocation • Participants are people used in psychological research • The way participants are selected for a research study and allocated to a group is very important
  4. 4. Population • The term population refers to the entire group of research interest from which a sample is drawn. • What is an example of a population?
  5. 5. Sample • The process of selecting participants for research is called sampling • The participants being studied in the research are called the sample. A sample is a subsection, or smaller group, of research participants selected from a larger group (population) of research interest.
  6. 6. Sample and Population
  7. 7. • A sample is a subgroup of the population. Therefore the sample is smaller than the population.
  8. 8. • A sample is a subgroup of the population. Therefore the sample is smaller than the population.
  9. 9. • A sample is a subgroup of the population. Therefore the sample is smaller than the population.
  10. 10. • A sample is a subgroup of the population. Therefore the sample is smaller than the population. • It is important that the sample accurately reflects, or is representative of the population it is taken from. Why?
  11. 11. • A sample is a subgroup of the population. Therefore the sample is smaller than the population. • It is important that the sample accurately reflects, or is representative of the population it is taken from. Why?
  12. 12. • A sample is a subgroup of the population. Therefore the sample is smaller than the population. • It is important that the sample accurately reflects, or is representative of the population it is taken from. Why?
  13. 13. • A sample is a subgroup of the population. Therefore the sample is smaller than the population. • It is important that the sample accurately reflects, or is representative of the population it is taken from. Why? • A representative sample allows the psychologist to be more confident in generalising the findings
  14. 14. Generalising • Extending or applying the results for a sample more widely to the population from which the sample was drawn
  15. 15. Sampling Procedures The following procedures ensure a sample is fairly representative of the population it was taken • Random sampling • Stratified sampling
  16. 16. Random Sampling • Random sampling ensures every member of the population of research interest has equal chance of being selected as a participant for a study • What method could you use to achieve a random sample? • Complete random sample? Is it representative?
  17. 17. Stratified sampling • In some research studies it is important to ensure that a particular groups in a population of interest are represented in their known proportions in that population • For example, if a psychologist wanted to understand Australians attitudes to sex before marriage, they would reasonably expect that peoples attitude would differ depending on their religion.
  18. 18. Stratified sampling • Stratified sampling involves dividing the population to be sampled into distinct subgroups, or strata, then selecting a different a separate sample from each strutum (subgroup), in the same proportions as they occur in the target population. • Income, age, sex, religion and IQ are examples of characteristics that may be used as the bais of dividing a population into a strata
  19. 19. Stratified random sample • Same as stratified sample, but after the people within each stratum are identified , random samples of proportionate size are drawn from within each of the strata (subgroups)
  20. 20. Obtaining a stratified random sample • Step 1 - Count the total number of people in the population • Step 2 - Count the number of people in each religious group • Step 3 - Calculate the percentage of each religion in the population using the following formula Number of people in a religion divided by Total number of people in the population X 100 • Step 4 - Create a stratified random sample of 10 people based on the percentages (that is proportions) of religions in the population
  21. 21. Revision • What would you like me to go over on Thursday?
  22. 22. Participant Allocation Participant allocation involves the way in which participants are assigned to the various conditions in a study. This process needs to be performed in a systematic way so that there is a balance of participants’ personal characteristics in the groups, preventing any potential confounding variables.
  23. 23. Control Group The control group is the group of participants, which is matched in all ways possible with the subject characteristics and conditions of the experimental group except that it is not exposed to the independent variable. What is the purpose if this group? This group serves as a baseline measure for comparison with the experimental group. The control group helps the researcher to determine if the independent variable did, in fact, cause an effect on the dependent variable.
  24. 24. Experimental Group The experimental group is the group of participants, which is matched in all ways possible with the participant characteristics and conditions of the control group but is also exposed to the independent variable. The purpose of the experimental group is to provide a measure of the influence in the dependent variable produced by the intervention.
  25. 25. Random Allocation • In random allocation, participants selected for the experiment are as likely to be in one group as the other. • What is the difference between random sampling and random allocation
  26. 26. • If you were going to perform a MRI scan on a 14 year old boy, what two ethical concerns would you need to consider? This needs to be explained in an extra- normal video. (5 Marks)

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