Sampling

• Target Population

  The group that the researchers draws the sample from and wants to be able to generalise the findings to.
• Why is it important the sample is representative

  So it is free from bias and can be generalised.
• Random Sampling

  • Very common method
  • Every person in the population has an equal chance of being selected
  • Selection must be unbiased
• Advantages of random sampling

  It is the only sampling method that ensures we have gained sample in an unbiased way
• Disadvantages of random sampling

  The group you end up with might be unrepresentative, for example you could pick people with good memory in a memory test
• Opportunity Sampling


  This is where you pick those who are easily available to be studied. You ask the people in your school. Anyone who agrees to take part forms your sample.
• Advantages of Opportunity Sampling

  • it is easier to get a sample
  • It is very widely used in psychology, researchers tend to use the students at the university where they work
• Disadvantages of Opportunity Sampling

  • A high chance of bias - the researcher may choose people he/she would want they are the same type of people anyway
• Self Selected Sample


  Volunteers

  The Ps select themselves e.g. replying to an advertisement
• Advantages of a Self Selected Sample

  Sample selects itself so easy for researcher
• Disadvantages of Self Selected Sample

  Majority of people unlikely to respond

  Biased sample - those who may respond could be a similar type of person, e.g. more conforming and show demand characteristics
• Systematic Sample

  Select Ps at fixed intervals every x'th person. If you have 75 people and have a sample of 15

  You would do 75/3 and select every 5th person
• Advantages of systematic samples

  Fairly unbiased
• Disadvantages of systematic sampling

  Not truly random
• Stratified Sampling


  This is one that is in proportion to those in the population. Say there were 100 teachers in a school, but only 20 males, you would decide how many people you would want in the sample, such as 10 then make the ratio in this case 2:8
• Advantages of Stratified Sampling

  The sample is proportionate to the population so is representative

  As a random sample is used it is fairly unbiased
• Disadvantages of Stratified Sampling

  Time consuming

  Expensive