3 Outlines:IntroductionSampling termsTypes of Sampling-Probability1-Simple random sample2-Stratified random sample3-Cluster sampling4-Systematic sampling-Non- probability1-Convenience sampling2-Quota sampling3-Purposive or judgmental sampling
4 Introduction:- The first two questions most researchers ask once a research has been defined are '' howmany subjects will I need to complete my study?''and '' how will I select them?''.
5 Sampling terms:-Sampling: - is a process of selection a portion ofthe population to obtain data regarding a problem.Population: - is a group of subjects havingcommon characteristics. The population mayconsist of events, animals, places, and individuals.The target population: - is the population understudy which the researcher wants to generalizethe research findings.
6 Types of Sampling:-There are two types of sampling probability & non-probability.Probability sampling includes the following:-1-Simple random sample.2-Stratified random sample.3-Cluster sampling.4-Systematic sampling.
7 Non-probability sampling includes the following:- 1- Convenience sampling.2- Purposive sampling.3- Quota sampling.
8 Probability Sampling:- Probability sampling: is a process of selectinga representative sample of the target population.Its purpose is to ensure that each element has anequal, and independent.
9 *Four types of probability sampling designs are:- 1- Simple Random Sample:-The simplest form of random sampling is called simplerandom sample.It is characterized by:-An independent chance for each element to be selectedinto the study.A complete list of the accessible population.A one-stage selection process. To start, the researcheridentifies the target population. Then list of all elementsof the target population (sampling frame), the next task israndomly selected the participants.
10 Methods of collection:- 1-Placing the number in a bowl and drawing out the numbers one at time.2-Using a table of random members.3-Using a computer –generated selection of random members.
11 Advantages of simple random sampling:- It eliminates researcher bias.Require limited knowledge about population.Provides a means for estimating sampling error.
12 Disadvantages of simple random sampling:- A complete list of the accessible population is needed.Very time consuming unless the computer is used to assist in the process.Need a large sample size.
13 2- Stratified Random Sampling:- In stratified sampling, subjects are chosen so that certainsubgroups (two or more strata) in the target populationwill be represented in the sample.Strata are determined by mutually exclusive variablessuch as gender, age, and educational level. After thepopulation divided, a simple random sample is takenwithin each stratum.It is used to ensure representatives of different groupswithin the population.
14 Advantages of stratified random sample:- Ensure the representation of a particular segmentof population.Disadvantages of stratified random sample:-It requires extensive knowledge of the populationunder the study to stratify it accurately.A complete list of a target population is needed.It can be quickly but very complex and timeconsuming.
15 3- Systematic Sampling:- It refers to a sampling strategy that involves theselection of every case drawn from a populationlist at fixed interval.First; the listing the population must be random inrelation to the variable of interest .Systematicrandom sampling can be conducted when anordered list of all members of the population isavailable.
16 Second; the first element or member of the sample must be selected randomly.The sampling interval; is the standarddistance between the elements chosen forthe sample.
17 Advantages of systematic random sample:- It is a fast, easy, and inexpensive way to draw a probability sample.Its simplicity may be reducing error.
18 Disadvantages of systematic random sample:- Not suitable in large or small number of population.Some time we can't obtain required sample size.
19 4- Cluster Sampling:-In cluster sampling, a sampling frame isdeveloped that includes a list of all the states,cities, institutions with which elements of theidentified population would be linked.
20 A randomized sample of these states, cities, institutions, or organizations would then be usedin the study. In some cases, this randomizedselection continues through several stages and isthen referred to as '' multistage sampling''.
21 For ex. The researcher might first randomly select states, then randomly select cities, withinthe sample states, then randomly select hospitalswithin selected cities, then randomly select thepatient on nursing unit who fit the criteria for thestudy within selected hospitals.
22 Advantages of cluster sample:- It is economical.It is particularly when the population is large and geographically dispersed.
23 Disadvantages:-More sampling errors tend to occur than other type of sampling.The appropriate handling of the statistical data from cluster sampling is very complex.
24 Non-probability Sampling:- Non-probability sampling; is an alternativeapproach to probability sampling , becauserandom selection is not used, the sample may notbe representative of a large population , and thusthe results can't be generalized beyond thesample study.
25 There are three types are:- 1- Convenience Sampling:-Is the uses participant who are easily accessibleto the researcher and who meet the criteria of thestudy.For ex. Take all patient admitted in surgicaldepartment with a particular diagnosis during thismonth.
26 Advantages:-It easier for researcher to obtain subjects.Save in time and money.Disadvantages:-The potential for sampling bias.The use of a sample that may not represent population.The limited generalization of the results.
27 2- Quota Sampling:-Quota sampling is similar to stratified randomsampling in that participants are divided into strata based on specific characteristics to provide representativeness of different groups within the population.Quota sampling differs from stratified randomsampling is that the participants are not randomly selected from each strata.
28 3- Purposive or Judgmental Sampling:- It involves the conscious selection by theresearcher of certain subjects or elements toinclude the study.A purposive sampling is used also when a highlyunusual group is being studied such asa population with a rare genetic disease.It used to describe lived experience of particularphenomena (postpartum depression).
29 Advantages:-Its allowance for the researcher to '' hand-pick''the sample based on knowledge of thephenomena of the study.
30 Disadvantages:-The potential for sampling bias.Uses of sample that dose not represent the population.The very limited to generalization of results.