Sampling methods ppt
- 2. sampling The process of selecting a number of individuals for a study in such a way that the individuals represent the larger group from which they were selected Sampling is the process of selecting observation(samples)to provide adequate and inference of the population
- 6. Types of sampling Probability sampling Non probability sampling
- 7. Probability sampling It is the method of sampling in which each element has known probability of being included in the sample Types of probability sampling 1.simple random sampling 2.stratified random sampling 3.systematic sampling 4.multi stage sampling 5.cluster sampling
- 8. Simple Random Sampling Selecting subjects so that all members of a population have an equal and independent chance of being selected It can be done by drawing the names out of a container until required number is reached There are two types :-simple random sampling with replacement simple random sampling without replacement
- 9. Simple random sampling Advantages 1. Easy to conduct 2. High probability of achieving a representative sample 3. Meets assumptions of many statistical procedures Disadvantages 1. Identification of all members of the population can be difficult 2. Contacting all members of the sample can be difficult
- 10. Systematic sampling It is modified form of simple random sampling It involves selecting a random element and then every nth element is selected until desired number of sample required For eg:- from population of 2000 if a sample of 100 is required ,then every 20th person can be selected If N is the total number of the wider population and “sn” is the required number in sample ,then “f” the frequency interval can be calculated as f=N/sn
- 11. Systematic sampling Advantages 1.Moderate cost 2.Simple to draw the sample Disadvantages 1.Periodic ordering required
- 12. Stratified sampling It is the two stage process 1.Devide the wider population into homogeneous(by identifying their characteristic) 2.Randomly select the sample within the groups Homogeneous groups are known as strata https://youtu.be/47bYUQ4Ueb8
- 13. Stratified sampling Proportionate random sampling-select cases in such a way that ensure the same proportion from each stratum in the sample Population:4% black,25%latino,27%Asian,44%white In sample of 1000:40 black,250latino,270Asian ,440 white Disproportionate random sampling-proportion selected from each stratum is not the same as in the population Population:4% black,25%latino,27%Asian,44%white In sample of 1000:250 black,250latino,250Asian ,250 white
- 15. Cluster sampling It is sample technique in which the population is divided in to clusters. Clusters are heterogeneous intact group of members of the population Then a sample of cluster is selected randomly from these clusters It is used when population is large Eg:- area sampling
- 16. Cluster sampling Advantages 1.Lower field/resource cost 2.Enable sampling of groups of individual for which detail on individual themselves may not be available Disadvantages 1.Lowest precision 2.Introduce more complexity in analysing data
- 18. Multi stage sampling It is the sampling method in which various sampling methods are used in different stages of sampling Eg :-a national polling service may stratify the country by geographical region, select a random sample of cities from each region and then interview a cluster of residence in the city
- 19. Multi-stage sampling Advantages 1.More accurate 2.More effective Disadvantages 1.Costly 2.Each stages in sampling introduce errors, so more stages more error will occur
- 20. Non probability sampling non probability sampling does not allow the researcher to determine the probability of each element to be in he sample Types of non probability sampling Incidental sampling Purposive sampling Judgmental sampling Snowball sampling
- 21. Incidental/convenience sampling The sampling involves selection of nearest individual or those whom the researcher meet in sample It is the process of picking up the people in most convenient and fastest way to immediately get their reaction to a certain or controversial issues Not representing target population because samples are selected if they can be assessed easily and conveniently It could deliver accurate result only when the population is homogeneous Advantage –easy to use Disadvantage-bias is present
- 22. Purposive/judgmental sampling The samples are selected for a particular purpose It is often featured in qualitative research For example, if the researchers want to study about the factors leads to sickle cell anaemia ,the only people to be consulted for first hand information are medical doctors who are treating such people
- 23. Purposive sampling Advantages 1.Flexible 2.Facilitate the purpose of study Disadvantages 1.Biased 2.Not reliable 3.Inaccuracy and inability in generalisation
- 24. Snowball sampling A sampling technique in which the existing subject recruits the future subjects from their acquaintances Sample group appears t grow like rolling snowball, as the sample built ups the enough data gathers from it Used for hidden population like drug users, persons with socially unacceptable behaviour, commercial prostitutes
- 25. Snowball sampling ADVANTAGES The chain referral process allows the researcher to reach populations that are difficult to sample when using other sampling methods Cheap, simple and cost-efficient Little planning and fewer workforce compared to other sampling techniques DISADVANTAGES Little control over the sampling method Representativeness of the sample is not guaranteed
- 27. Thank you……..