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Sampling methods PPT


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Sampling methods PPT

  1. 1. ByVijay Mehta
  2. 2. What exactly IS a “sample”?
  3. 3. What do qualitative researchers worry about? II want to show want to showII want to see II really want my really want my want to see II want to want to how social how socialthe world research research the world describe the describe the change occurs. change occurs.through the approach to be approach to be through the context in a lot context in a lot I’m interested in I’m interested ineyes of my flexible and flexible and eyes of my of detail. of detail. how things come how things comerespondents. able to change. able to change. respondents. to be. to be.
  4. 4. Social actors are notSocial actors are notpredictable like objects.predictable like objects. Randomized events are Randomized events are irrelevant to social life. irrelevant to social life. Probability sampling is Probability sampling is expensive and inefficient. expensive and inefficient. Non-probability sampling is the Non-probability sampling is the best approach. best approach.
  5. 5. Types of samples
  6. 6. Simple Random Sample Get a list or “sampling frame” a. This is the hard part! It must not systematically exclude anyone. Generate random numbers Select one person per random numbers
  7. 7. Systematic Random Sample Select a random number, which will be known as k Get a list of people, or observe a flow of people (e.g., pedestrians on a corner) Select every kth person  Careful that there is no systematic rhythm to the flow or list of people.  If every 4th person on the list is, say, “rich” or “senior” or some other consistent pattern, avoid this method
  8. 8. Stratified Random Sample1. Separate your population into groups or “strata”2. Do either a simple random sample or systematic random sample from there a. Note you must know easily what the “strata” are before attempting this b. If your sampling frame is sorted by, say, school district, then you’re able to use this method
  9. 9. Multi-stage Cluster Sample Get a list of “clusters,” e.g., branches of a company Randomly sample clusters from that list Have a list of, say, 10 branches Randomly sample people within those branches  This method is complex and expensive
  10. 10. The Convenience Sample Find some people that are easy to find
  11. 11. The Snowball Sample Find a few people that are relevant to your topic. Ask them to refer you to more of them.
  12. 12. The Quota Sample Determine what the population looks like in terms of specific qualities. Create “quotas” based on those qualities. Select people for each quota.
  13. 13. The Theoretical Sample
  14. 14. Accidental sampling A type of nonprobability sampling which involves the sample being drawn from that part of the population which is close to hand The researcher using such a sample cannot scientifically make generalizations about the total population In social science research, snowball sampling is a similar technique
  15. 15. Panel sampling The method of first selecting a group of participants through a random sampling Period of data collection is called a "wave“ Panel sampling can also be used to inform researchers about within-person health changes due to age
  16. 16. How many? Qualitative researchers seek “saturation”  “How many” isn’t the issue. Do you understand the phenomenon? Have you learned enough?  Mere numbers are irrelevant. You want “verstehn” or deep understanding Quantitative researchers seek statistical validity  Can you safely generalize to the population? Have you systematically excluded anyone? (See the “famous sampling mistake”)
  17. 17. Improving Response Rates Personalize the invitation Offer money -- no strings attached
  18. 18. ThankYou all