sampling.pptx
- 1. Sample
- 2. What Is a Sample? A sample refers to a smaller, manageable version of a larger group. It is a subset containing the characteristics of a larger population. Samples are used in statistical testing when population sizes are too large for the test to include all possible members or observations. A sample should represent the population as a whole and not reflect any bias toward a specific attribute.
- 3. • Using samples allows researchers to conduct their studies easily and in a timely fashion. • In order to achieve an unbiased sample, the selection has to be random so everyone from the population has an equal and likely chance of being added to the sample group.
- 4. Sampling is the process of selectingobservations (a sample) to provide an adequate description and deduction of the population. Sample It is aunit that is selected from population Represents the whole population Purpose to draw theconclusion WhySample??? Sampling Frame Listing of population from which asample ischosen Sampling
- 5. Population Sample Sampling Frame Sampling Process What you want to talk about What you actually observe in the data conclusion
- 10. All subsets of the frame are given an equal probability. Random number generators
- 11. Advantages: Minimal knowledge of population needed Easyto analyze data Disadvantages: Low frequency of use Doesnot useresearchers’expertise Largerrisk of randomerror
- 12. Population is divided into two or more groups called strata Subsamples are randomly selected from each strata
- 13. Advantages: Assuresrepresentation of all groups i n sample population Characteristics of each stratum canbe estimated and comparisons made Disadvantages: Requires accurate information on proportions of eachstratum Stratified lists costly to prepare
- 14. Thepopulation is divided into subgroups (clusters) like families. Asimple random sample is taken from eachcluster
- 15. Advantages: Canestimate characteristics of both cluster and population Disadvantages: Thecost to reach an element to sample i s very high Eachstage in cluster sampling introduces sampling error—the more stagesthere are, the more error there tends tobe
- 16. Order all units in the samplingframe Then every nth number on the list isselected N=Sampling Interval
- 17. Advantages: Moderate cost; moderate usage Simple to drawsample Easytoverify Disadvantages: Periodic ordering required
- 18. Carried out in stages Using smaller and smaller sampling units at each stage 1 2 3 4 5 6 7 8 9 1 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 P r i m a r y S e c o n d a r y C l u s t e r s C l u s t e r s S i m p l e R a n d o m S a m p l i n g w i t h i n S e c o n d a
- 19. Advantages: More Accurate More Effective Disadvantages: Costly Each stage in sampling introduces sampling error—the more stages there are, the more error there tends tobe
- 21. Theprobability of each casebeing selected from t h e total population is not known. Units of the sample are chosen on the basisof personal judgment or convenience. There are NOstatistical techniques for measuring random sampling error in anon-probability sample.
- 22. A. Convenience Sampling B.Quota Sampling C.Judgmental Sampling (PurposiveSampling) D.Snowball sampling E.Self-selection sampling
- 23. Convenience sampling involves choosing respondents at the convenience of theresearcher. Advantages Very low cost Extensively used/understood Disadvantages Variability and bias cannot be measured or controlled Projecting data beyond sample not justified Restriction of Generalization.
- 25. Thepopulation is first segmented into mutually exclusive sub-groups, just asin stratified sampling. Researchers choose these individuals according to specific character or qualities.
- 26. Advantages Usedwhen research budget is limited Very extensively used/understood No need for list of populationelements Disadvantages Variability and bias cannot be measured/controlled Time Consuming Projecting data beyond sample not justified
- 27. Researcheremploys his or her own "expert” judgment about. Advantages There is aassuranceof Quality response Meet the specificobjective. Disadvantages Biasselection of sample mayoccur Time consuming process.
- 28. Theresearch starts with akeyperson and introduce the next one to becomeachain Advantages Low cost Useful in specific circumstances & for locating rare populations Disadvantages Not independent Projecting data beyond sample not justified
- 29. It occurs when you allow each caseusually individuals, to identify their desire to take part in the research. Advantages More accurate Useful in specific circumstances to serve thepurpose. Disadvantages More costly due toAdvertizing Massare left
- 30. SAMPLING ERRORS
- 31. Theerrors which arise due to the useof sampling surveysare known asthe sampling errors. Twotypes of samplingerrors Biased Errors- Dueto selection of sampling techniques; sizeof the sample. Unbiased Errors / Random sampling errors- Differences between the members of the population included or not included.
- 32. Specific problem selection. Systematic documentation of relatedresearch. Effective details. Effective pre testing. Controlling methodological bias. Selection of appropriate samplingtechniques.
- 33. Non-sampling errors refers to biasesand mistakes in selection of sample. CAUSES FOR NON-SAMPLING ERRORS Sampling operations Inadequate of response Misunderstanding the concept Lackof knowledge Concealment of the truth. Loaded questions Processing errors Sample size