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Non probability sampling process

This video explains about different types of non probability sampling methods

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Non probability sampling process

  1. 1. Non Probability Sampling Srividhya.N
  2. 2. Introduction Generally it is believed that non random methods of sampling are more likely to produce lot of bias. But in nursing research most of the time non random sampling techniques are used.
  3. 3. Definition Non probability sampling is a technique where in the samples are gathered in a process that does not give all the individuals in the population equal chances of being selected
  4. 4. Features ● No equal chance for participation ● Time limitation in studies may affect probability sampling technique ● Subjects are selected on the basis of purpose and availability ● Cannot be used in generalization
  5. 5. Uses ● Study related to particular trait ● Used in qualitative,exploratory or Pilot study ● Used when random sampling method is not possible ● Used when the researcher has limited budget
  6. 6. Types of non probability sampling method ● Purposive sampling ● Convenience sampling ● Volunteer sampling ● Consecutive sampling ● Quota sampling ● Snowball sampling ● Genealogy sampling
  7. 7. Purposive sampling Subjects are chosen to be a part of the sample with a specific purpose in mind It is otherwise known as judgemental sampling In this method samples are chosen by choice not by chance Example: A study to assess the post disaster depression among people living in tsunami affected area in TamilNadu.
  8. 8. Advantages ● Simple to draw sample ● Saves resources Disadvantages ● Requires considerable knowledge about population ● Conscious bias may occur ● Not reliable
  9. 9. Convenience sampling Subjects are chosen because of their convenient accessibility and proximity to the researcher Most commonly used Fast and inexpensive sampling method It is otherwise called as accidental sampling Example : A study on diabetic people visiting an hospital....and the researcher select his sample from govt hospital Payyanur as he is residing near that hospital.
  10. 10. Hey , are you willing to join the study?
  11. 11. Advantages ● Easy to select sample ● Cost effective ● Less time consuming ● Saves money and resources Disadvantages ● Sampling bias ● Sample is not representative of entire population ● Not a true representative ● Cannot be generalized
  12. 12. Volunteer sampling Target subjects are informed through mass media to participate in study and interested participants may voluntarily contact researcher.
  13. 13. Example: The researcher if interested to assess the effectiveness of a selected yoga technique in hypertension. So she gives an advertisement for participation in scheduled yoga classes and does pre and post assessment
  14. 14. Advantages ● Needs minimal effort ● Cost effective ● Used to collect large sample size Disadvantages ● Sampling bias and error ● Not a true representative ● Cannot be generalized
  15. 15. Consecutive sampling Picks up all the available subjects who are meeting the preset inclusion and exclusion criteria Also known as enumerative sampling Similar to convenient sampling technique One of the best in non random sampling method Example: A researcher want to study a lifestyle of patients with post coronary catheterization , he will select all patients admitted during a month in particular hospital.
  16. 16. Advantages ● Little effort ● Inexpensive ● Less time consuming ● More representatives Disadvantages ● No clarification on sample size and shedule ● No guarantee on enough sample ● Lack of generalizability
  17. 17. Quota sampling It is a non random sampling technique in which the researcher ensures equal or proportionate representation of subjects depending on the trait. Like on the basis of age, sex, education, race , religion etc. It resembles stratified sampling Example. Researcher wants to a study the effectiveness of online education in nursing ,since take 25 samples from each year in that institution.
  18. 18. Advantages ● Cheaper ● Suitable for fieldwork studies. Disadvantages ● Does not guarantee enough sample ● Sampling error and bias possible
  19. 19. Snowball sampling Snowball sampling or chain-referral sampling is defined as a non- probability sampling technique in which the samples have traits that are rare to find. This is a sampling technique, in which existing subjects provide referrals to recruit samples required for a research study.
  20. 20. Types Linear snowball : In linear sampling it starts with one person and that person bring one sample and it goes till the researcher gets enough sample size Exponential snowball sampling: In this type one sample refer two or many samples at a time till the achieved sample size met.
  21. 21. Advantages ● Quicker to find sample ● Coast effective ● Sample hesitant subjects Disadvantages ● Sampling bias ● Lack of cooperation
  22. 22. Genealogy Sampling It is a sampling method in which a entire family or lineages are involved in research This sampling method is commonly used to study hereditary or genetic abnormalities Example: The researcher is interested to study presence of oncology disease in a family and so he will select All the members in that family.
  23. 23. Difference between probability and non probability method Basis for comparison ➢ Definition ➢ Alternately known ➢ Basis for selection ➢ Result ➢ Inferences ➢ Hypothesis ➢ Method Probability sampling ➢ Definition ➢ Random sampling ➢ Randomly ➢ Unbiased ➢ Statistical ➢ Tested ➢ Objective Non probability ➢ Definition ➢ Non random ➢ Arbitrarily ➢ Biased ➢ Analytical ➢ Generated ➢ Subjective
  24. 24. Summary Non probability sampling method ● Purposive sampling ● Convenience sampling ● Volunteer sampling ● Consecutive sampling ● Quota sampling ● Snowball sampling ● Genealogy sampling
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