sampling (non probability) research ppt.pptx

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1. NON- PROBABILITY SAMPLING

2. Non-probability sampling technique is a technique wherein the sample are gathered in a process that does not give all the individuals in the population equal chances of being selected in the sample. In other words, in this type of sampling every subject does not have equal chance to be selected because elements are chosen by choice not by chance through non random sampling methods.

3. In non random sampling, certain elements have more probability to be the part of sample while others may have no chance of being included in the sample. This restricts the generalization that can be made about the study findings .

4. It is generally observed that despite the limitations of non probability sampling, most of the nurse researchers use these sampling techniques .

5. FEATURES OF NON PROBABILITY SAMPLING Non probability sampling is a technique wherein the sample are gathered in a process that does not give all the individuals in the population equal chance of being selected. In any form of research, true random sampling is always difficult to achieve. Most researcher are bound by time, money or workforce and because of these limitations, it is difficult to randomly sample the entire population and it is often necessary to employ another sampling technique.

6. CONT……. In contrast with probability sampling, non probability sample is not a product of a randomized selection process. Subjects in a non probability sample are usually selected on the basis of their accessibility or by the purposive personal judgement of the researcher.

7. CONT……. The downside of this is that an unknown proportion of the entire population is not sampled. This entails that the sample may or may not represent the entire population accurately. Therefore, the results of the researcher cannot be used in generalizations pertaining to the entire population.

8. USES OF NON PROBABILITY SAMPLING This sampling type can be utilized when it is needed to show that a particular trait is existent in the population. It can also be utilized when the researcher targets to make a qualitative, pilot, or exploratory study. When random sampling is impossible like when the population is almost limitless, it can also be used.

9. CONT….. Moreover when the research does not aim to produce results that will be utilized to generate generalizations pertaining to entire population, it can be used. In addition, when the researcher has got limited budget , time, workforce, it is also of use. Used as a random sampling or, probability sampling, this technique can also be used in an initial study(pilot study) and can be carried out again.

10. TYPES OF NON PROBABILTY SAMPLING Purposive sampling Convenience sampling Volunteer sampling Consecutive sampling Quota sampling Snowball sampling Genealogy sampling

11. PURPOSIVE SAMPLING It is more commonly known as “judgmental” or ‘authoritative sampling’. In this type of sampling, subjects are chosen to be part of the sample with a specific purpose in mind. In purposive sampling the researcher believes that some subjects are fit for research compared to other individuals. This is the reason why they are purposively chosen as subjects.

12. USES OF PURPOSIVE SAMPLING Requires in depth knowledgeable about the accessible population. Used when a limited number of individuals possess the trait of interest.

13. FOR EXAMPLE A researcher want to study the lived experiences of post disaster depression among people living in earthquake affected areas of Gujarat. In this case, those subjects are selected who were the victims of the earthquake disaster and have suffered post disaster depression living in earthquake affected areas of Gujarat. For this study researcher selected only those people who fulfil the criteria as well as particular subjects that are the typical and representative part of population as per researcher knowledge.

14. ADVANTAGES Simple to draw sample and useful in explorative studies. Save resources, require less fieldwork.

15. DISADVANTAGES Requires considerable knowledge about the population under study. It is not always reliable sample, as conscious bias may exist. The two important weaknesses of purposive sampling stay with the authority and in the sampling process, both of which relate to the bias and reliability that accompanies the sampling technique.

16. CONT….. In order to determine the reliability of the expert or the authority, there is usually no way. Because of the experts, it is best to ignore sampling error to opt the most experienced and best authority in the field of interest.

17. CONVENIENCE SAMPLING Covenience sampling is probably the most common of all sampling techniques because it is fast, inexpensive, easy and the subjects are readily available. In this sampling technique subjects are selected due to their convenient accessibility and proximity to the researcher. The subjects are chosen because of the fact they are very easy to recruit for the study. Sometime it is also known as accidental sampling.

18. USES OF CONVENIENCE SAMPLING Researcher use convenience sampling not just because it is easy to use, but also because it also has other research advantages. In pilot studies, convenience sampling is usually used because it allow the researcher to obtain basic data and trends for his study without the complications of using random sample selection methods. In addition, this sampling technique is also useful in documenting a particular quality of a substance or phenomenon that occurs within a given sample.

19. FOR EXAMPLE If a researcher want to conduct a study on the older people residing in Ludhiana, the researcher observes that he can meet several older people coming for morning walk in a park located near his residence in Ludhiana, he can choose these people as his research subjects. These subjects are readily accessible for the researcher and may help him to save time, money, and resources .

20. ADVANTAGES This technique is considered easiest, cheapest, and least time consuming. This sampling technique may help in saving time, money and resources.

21. DISADVANTAGES The most obvious criticism about convenience sampling is sampling bias, and that the sample is not representative of the entire population. It does not provide the representative sample from the population of the study. Findings generated from these samples cannot be generalized on the population.

22. VOLUNTEER SAMPLING In this sampling technique , in which participants themselves volunteer to participate in the study and they only approach the researcher to be the part of study sample. Researcher publishes an advertisement or informs target population through mass media to participate in the study and interested participants may voluntarily contact researcher to participate in the study.

23. FOR EXAMPLE A nurse researcher is interested to assess the effectiveness of a selected yoga technique on the reduction of blood pressure. She may advertise in newspaper to inform target people to participate in this research to take the scheduled yoga classes and pre and post assessment of blood pressure. In this instance, interested people may voluntarily contact researcher to participate in the study.

24. ADVANTAGES Cost effective sampling technique. Needs very limited efforts and time to locate the study participants. This technique helps to collect large size data in limited time period.

25. DISADVANTAGES Only interested people contact to participants, so there are very chances that sample may not be a representative sample. It encounter the systematic error or bias because only people who have the assess to particular medium of receiving the researcher’s published advertisement may get a chance to participate in the study, the rest will be left unrepresented .

26. CONT……… Since there are very high chances of non representative of sample and systematic bias, the study results lack the generalizability.

27. CONSECUTIVE SAMPLING Consecutive sampling is very similar to convenience sampling technique except that it seeks to include all accessible subjects as part of the sample. This sampling technique considered as the most best because it includes all the subjects that are available, which make the sample a better representation of the entire population. It is also known as total enumerative sampling.

28. CONT…… In this sampling technique the investigator picks up all the available subjects who are meeting the preset inclusion and exclusion criteria This technique is generally used in small sized populations.

29. FOR EXAMPLE If a researcher wants to study the activity pattern of post kidney transplant patient , he can select all post kidney transplant patients who meet the designed inclusion and exclusion criteria, and who are admitted in post transplant ward during a specific time period.

30. ADVANTAGES There is very little effort on the part of the researcher when performing this sampling technique. It is not expensive, not time consuming, and not workforce intensive. Ensure more representativeness of the selected sample.

31. DISADVANTAGES The researcher has no set plans about the sample size and sampling technique. It always does not guarantee the selection of representative sample. Results from this sampling technique cannot be used to create conclusions and interpretations pertaining to the entire population .

32. GENEALOGY SAMPLING In this sampling technique all the members of entire related families are selected rather than selecting the different households in the village or area. The genealogy sampling begin with identifying a first participant, who is convinced to participate in the study and further he/she is asked to refer to close relatives of his family, who even may be living in other areas or villages.

33. CONT….. This sampling technique is primarily used in rural population, which are socio-culturally and economically homogenous, and it is frequently used in genetic studies to identify trends of genes in traditional families and so on. This sampling technique provides significant cross sectional of selected community by age, gender, and so on.

34. ADVANTAGES This sampling technique is useful in drawing a representative sample from traditional rural communities, which are socio-culturally and economically homogenous. Saves the time and efforts in locating the study subjects because participants are identified through reference from previous participants.

35. DISADVANTAGES This sampling technique encounter problem of systematic errors or bias. It lacks the diversity of sample participant characterstics because subjects are selected from a family or related families. Thus , it has limited usefulness.

36. QUOTA SAMPLING Quota sampling is a non probability sampling technique wherein the researcher ensures equal or proportionate representation of subjects, depending on which traits is considered as the basis of the quota.

37. STEPS AND USES OF QUOTA SAMPLING Dividing the population into exclusive subgroups is the initial step in non probability quota sampling. Thereafter the researcher should recognize the proportions of these subgroups in the population; this same proportion will be employed in the sampling process. Finally the researcher choses subjects from various subgroups when taking into account the proportions noted in the previous step.

38. CONT…. The sample is representative of the entire population and is ensure by the final step .it also permits the researcher to study characterstics and traits that are significant for each subgroups. The main reason for choosing quota samples is that they permit the researchers to sample a subgroup that is of very large interest to the study.

39. FOR EXAMPLE If the basis of quota is college level and the researcher needs equal representation with a sample size of 100, he or she must select 25 first year students, another 25 second year students, 25 third year students and 25 final year students. The quota sampling technique appears like stratified random sampling technique; however in this sampling technique, sample is selected without random process from different quotas .

40. ADVANTAGES Economically cheap, as there is no need to approach all the candidates. Suitable for studies where the fieldwork has to be carried out, like studies related to market and public opinion polls.

41. DISADVANTAGES Although this kind of sampling technique is seen to be wholly representative of the population , still in some cases it is not so. Keeping in mind that only the chosen traits of the population were taken into consideration while performing the subgroups. Not possible to estimate errors. Bias is possible, as investigator/interviewer can select persons known to him.

42. SNOWBALL SAMPLING This sampling technique is used by researcher to identify potential subjects in studies where subjects are hard to locate, such as commercial sex workers, drug abusers etc. Researcher used this sampling methods if the sample for studies that are very rare or are limited to very small subgroups of the population. This is also known as chain referral sampling.

43. CONT….. The researcher ask for assistance from the subjects to identify people with a similar trait of interest after observing the initial subject. Asking subjects to nominate another person with the same trait is similar to the process of snowball sampling.until he or she obtains sufficient number of subjects, the researcher then observes the nominated subjects and continues in same way.

44. FOR EXAMPLE The researcher may choose to use snowball sampling while obtaining subjects for a study to observe a rare disease. It is also practical that the patients with similar disease may have a support group . Observing one of the members as your initial subject then leads to more subjects for the study.

45. TYPES OF SNOWBALL SAMPLING Linear snowball sampling In this each selected sample is asked to provide reference of only one similar subject, where a linear chain is created by the completion of desired sample.

46. CONT….. Exponential nondiscriminative snowball sampling In this, each sample member is asked to provide reference of at least two similar subjects, because of which the size of the sample grows exponentially and a large sample size can be achieved .

47. EXPONENTIA DISCRMINATIVESNOWBALLSAMPLING In this one sample is selected and asked for two references of similar subjects, out of which at least one subject must be active to provide further references and another could be nonactive in providing references. Each active reference subject is further asked for two references for similar subjects: out of them one should be active for further references .

48. ADVANTAGES When utilizing other sampling methods, the chain referral process permits the researcher to reach each populations that are difficult to sample. The process is simple cheap and cost efficient. This sampling technique requires lesser workforce and little planning as compared to other methods.

49. DISADVANTAGES The researcher have less control over the sampling method, the subject that the researcher can get depend chiefly on the previous subjects that were observed. Sample representativeness is not guaranteed. Regarding the true distribution of the population and of the sample, the researcher has no idea.