EDU702: RESEARCH EDU702: RESEARCH METHODOLOGYMETHODOLOGY

THE BASIC OF EDUCATIONAL THE BASIC OF EDUCATIONAL RESEARCHRESEARCH

SAMPLINGSAMPLING

DEFINITION: SAMPLINGDEFINITION: SAMPLING

The process of selecting a number of The process of selecting a number of individuals for a study in such a way individuals for a study in such a way that the individuals represent the that the individuals represent the larger group from which they were larger group from which they were selected.selected.

DEFINITION: POPULATIONDEFINITION: POPULATION

The larger group from which The larger group from which individuals are selected to participate.individuals are selected to participate.

TARGET VERSUS TARGET VERSUS ACCESSIBLE POPULATIONS:ACCESSIBLE POPULATIONS:

11.. The Target Population is the ideal selection of actual The Target Population is the ideal selection of actual population which researcher really like to generalize:population which researcher really like to generalize:

- is rarely available.- is rarely available.- Researcher’s ideal choice.- Researcher’s ideal choice.

2. The Accessible or ‘available’ population is the 2. The Accessible or ‘available’ population is the population to which a researcher is able to generalize:population to which a researcher is able to generalize:

- Researcher’s realistic selection- Researcher’s realistic selection

SAMPLING:SAMPLING:

1)1) RANDOM SAMPLING METHODRANDOM SAMPLING METHOD

2)2) NONRANDOM SAMPLING NONRANDOM SAMPLING METHODMETHOD

RANDOM SAMPLING RANDOM SAMPLING METHODSMETHODS

1.1. Simple Random SamplingSimple Random Sampling

2.2. Stratified Random SamplingStratified Random Sampling

3.3. Cluster Random SamplingCluster Random Sampling

4.4. Two-Stage Random SamplingTwo-Stage Random Sampling

SIMPLE RANDOM SAMPLINGSIMPLE RANDOM SAMPLING

The proces of selecting a sample that The proces of selecting a sample that allows induvidual in the defined allows induvidual in the defined population to have an equal and population to have an equal and independent chance of being selected independent chance of being selected for the sample.for the sample.

STEPS IN RANDOM SAMPLING:STEPS IN RANDOM SAMPLING:

1. 1. Identify and define the population.Identify and define the population.

2.2. Determine the desired sample size. Determine the desired sample size.

3.3. List all members of the population. List all members of the population.

4. 4. Assign all individuals on the list consecutive Assign all individuals on the list consecutive number from zero to the required number. number from zero to the required number. Each individual must have the same number Each individual must have the same number of digits as each other individual.of digits as each other individual.

STEPS IN RANDOM SAMPLING:STEPS IN RANDOM SAMPLING:

5.5. Select an arbitrary number in the table of Select an arbitrary number in the table of random numbers.random numbers.

6. 6. For the selected number, look only at the For the selected number, look only at the number of digits assigned to each population number of digits assigned to each population member.member.

STEPS IN RANDOM SAMPLING:STEPS IN RANDOM SAMPLING:

7.7. If the number corresponds to the number If the number corresponds to the number assigned to any of the individual in the assigned to any of the individual in the population, then that individual is included population, then that individual is included in the sample.in the sample.

8.8. Go to the next number in the column and Go to the next number in the column and repeat step #7 until the desired number of repeat step #7 until the desired number of individuals has been selected for the individuals has been selected for the

sample.sample.

ADVANTAGES OF SIMPLE ADVANTAGES OF SIMPLE RANDOM SAMPLING:RANDOM SAMPLING:

Easy to conductEasy to conduct

Strategy requires minimum Strategy requires minimum knowledge of the population to be knowledge of the population to be sampledsampled

DISADVATAGES OF SIMPLE DISADVATAGES OF SIMPLE RANDOM SAMPLING:RANDOM SAMPLING:

Need names of all population members.Need names of all population members.

May over-represent or under-estimate May over-represent or under-estimate sample members.sample members.

There is difficulty in reaching all selected There is difficulty in reaching all selected in the sample.in the sample.

STRATIFIED RANDOM STRATIFIED RANDOM SAMPLINGSAMPLING

The process of selecting a sample The process of selecting a sample that allows identified subgroups in that allows identified subgroups in the defined population to be the defined population to be represented in the same proportion represented in the same proportion that they exist in the population.that they exist in the population.

STEPS IN STRATIFIED STEPS IN STRATIFIED SAMPLING:SAMPLING:

1.1. Identify and define the population.Identify and define the population.

2.2. Determine the desired sample size.Determine the desired sample size.

3.3. Identify the variable and subgroups (strata) Identify the variable and subgroups (strata) for which you want to guarantee appropriate, for which you want to guarantee appropriate, equal representation. equal representation.

STEPS IN STRATIFIED RANDOM STEPS IN STRATIFIED RANDOM SAMPLINGSAMPLING

4. 4. Classify all members of the population as Classify all members of the population as members of the one identified subgroup.members of the one identified subgroup.

5.5. Randomly select, using a table of random Randomly select, using a table of random numbers; an “appropriate” number of numbers; an “appropriate” number of

individuals from each of the subgroups, individuals from each of the subgroups, appropriate meaning an equal number of appropriate meaning an equal number of individuals.individuals.

ADVANTAGES OF STRATIFIED ADVANTAGES OF STRATIFIED RANDOM SAMPLING:RANDOM SAMPLING:

More precise sample.More precise sample.

Can be used both proportions and Can be used both proportions and stratification sampling.stratification sampling.

Sample represents the desired strta.Sample represents the desired strta.

DISADVANTAGES OF DISADVANTAGES OF STRATIFIED RANDOM STRATIFIED RANDOM

SAMPLING:SAMPLING: Need names of all population members.Need names of all population members.

There is difficulty in reaching all selected There is difficulty in reaching all selected in the sample.in the sample.

Researcher must have names of all Researcher must have names of all populations.populations.

CLUSTER SAMPLINGCLUSTER SAMPLING

The process of randomly selecting The process of randomly selecting intact groups, not individuals, within intact groups, not individuals, within the defined population sharing the defined population sharing similar characteristics.similar characteristics.

STEPS IN CLUSTER RANDOM STEPS IN CLUSTER RANDOM SAMPLING:SAMPLING:

1.1. Identify and define the population.Identify and define the population.

2.2. Determine the desired sample size.Determine the desired sample size.

3.3. Identify and define a logical cluster.Identify and define a logical cluster.

STEPS IN CLUSTER RANDOM STEPS IN CLUSTER RANDOM SAMPLING:SAMPLING:

4.4. List all clusters (or obtain a list) that make up List all clusters (or obtain a list) that make up the population of clusters.the population of clusters.

5.5. Estimate the average number of population Estimate the average number of population members per cluster.members per cluster.

6. 6. Determine the number of clusters needed by Determine the number of clusters needed by dividing the sample size by the estimated dividing the sample size by the estimated size of a cluster.size of a cluster.

STEPS IN CLUSTER RANDOM STEPS IN CLUSTER RANDOM SAMPLING:SAMPLING:

7. Randomly select the needed number of 7. Randomly select the needed number of clusters by using a table of random clusters by using a table of random numbers.numbers.

8. Include in your study all population 8. Include in your study all population members in each selected cluster.members in each selected cluster.

ADVANTAGES OF CLUSTER ADVANTAGES OF CLUSTER RANDOM SAMPLING:RANDOM SAMPLING:

Efficient.Efficient. Researcher does not need nemes of Researcher does not need nemes of

all population members.all population members. Reduces travel to site.Reduces travel to site. Useful for educational research.Useful for educational research.

DISADVANTAGES OF CLUSTER DISADVANTAGES OF CLUSTER RANDOM SAMPLING:RANDOM SAMPLING:

Fewer sampling points make it less like Fewer sampling points make it less like that the sample is representative.that the sample is representative.

TWO-STAGE RANDOM TWO-STAGE RANDOM SAMPLINGSAMPLING

The process of COMBINING Cluster The process of COMBINING Cluster Random Sampling with an Individual Random Sampling with an Individual Random Sampling.Random Sampling.

STEPS IN TWO-STAGE RANDOM STEPS IN TWO-STAGE RANDOM SAMPLING:SAMPLING:

1.1. Select randomly 25 schools from 100 schools Select randomly 25 schools from 100 schools in the district. (Cluster) in the district. (Cluster)

ADVANTAGES OF TWO-STAGE ADVANTAGES OF TWO-STAGE RANDOM SAMPLING:RANDOM SAMPLING:

Less time-consumingLess time-consuming

DEFINITION OF NON RANDOM DEFINITION OF NON RANDOM SAMPLINGSAMPLING

Any sampling method where some Any sampling method where some elements of the population have no choice elements of the population have no choice of selection or where the probability of of selection or where the probability of selection cannot be accurately determined.selection cannot be accurately determined.

TYPES OF NON RANDOM TYPES OF NON RANDOM SAMPLING METHODSSAMPLING METHODS

1.1. Systematic SamplingSystematic Sampling

2.2. Convenience SamplingConvenience Sampling

3.3. Purposive SamplingPurposive Sampling

SYSTEMATIC SAMPLINGSYSTEMATIC SAMPLING

The process of selecting individuals The process of selecting individuals within the defined population from a within the defined population from a list by taking every list by taking every KKth name.th name.

**K = sampling interval**K = sampling interval (sometimes known as the (sometimes known as the skipskip))

STEPS IN SYSTEMATIC STEPS IN SYSTEMATIC SAMPLING:SAMPLING:

1.1. Identify and define the population.Identify and define the population.

2.2. Determine the desired sample size.Determine the desired sample size.

3.3. Obtain a list of the population.Obtain a list of the population.

4.4. Determine what Determine what KK is equal to by dividing the size of is equal to by dividing the size of the population by the desired sample size.the population by the desired sample size.

EquationEquation

K =K =

NN

nn

K = sampling interval

N = population size

n = sample size

STEPS IN SYSTEMATIC STEPS IN SYSTEMATIC SAMPLING:SAMPLING:

5. 5. Start at some random place in the population Start at some random place in the population list. Close your eyes and point your finger to list. Close your eyes and point your finger to a name.a name.

6.6. Starting at that point, take every Starting at that point, take every KKth name on th name on the list until the desired sample size is the list until the desired sample size is reached.reached.

7.7. If the end of the list is reached before the If the end of the list is reached before the desired sample is reached, go back to the top desired sample is reached, go back to the top of the list.of the list.

ADVANTAGES OF SYSTEMATIC ADVANTAGES OF SYSTEMATIC SAMPLING:SAMPLING:

Sample selection is simpleSample selection is simple

DISADVANTAGES OF DISADVANTAGES OF SYSTEMATIC SAMPLING:SYSTEMATIC SAMPLING:

All members of the population do not All members of the population do not have an equal chance of being selected.have an equal chance of being selected.

The The KKth person may be related to a th person may be related to a periodical order in the population list, periodical order in the population list, producing unrepresentativeness in the producing unrepresentativeness in the sample. sample.

CONVENIENCE SAMPLINGCONVENIENCE SAMPLING

The process of including whoever The process of including whoever happens to be available at the time . happens to be available at the time . It is also called “accidental” or It is also called “accidental” or “haphazard” sampling.“haphazard” sampling.

ADVANTAGE OF CONVENIENCE ADVANTAGE OF CONVENIENCE SAMPLING:SAMPLING:

the availability and the quickness with which the availability and the quickness with which data can be gathereddata can be gathered

DISADVANTAGES OF DISADVANTAGES OF CONVENIENCE SAMPLING:CONVENIENCE SAMPLING:

Difficulty in determining how much of Difficulty in determining how much of the effect (dependent variable) results the effect (dependent variable) results from the cause (independent variable)from the cause (independent variable)

the the riskrisk that the that the samplesample might not might not representrepresent the the populationpopulation as a whole, and it might be biased by as a whole, and it might be biased by volunteersvolunteers

PURPOSIVE SAMPLINGPURPOSIVE SAMPLING

The process whereby the researcher The process whereby the researcher selects a sample based on experience selects a sample based on experience or knowledge of the group to be or knowledge of the group to be sampled. It is also called sampled. It is also called “judgement” sampling.“judgement” sampling.

ADVANTAGE OF PURPOSIVE ADVANTAGE OF PURPOSIVE SAMPLINGSAMPLING

Useful for situations where you need to reach a Useful for situations where you need to reach a targeted sample quickly and where sampling targeted sample quickly and where sampling for proportionality is not the main concern.for proportionality is not the main concern.

DISADVANTAGES OF DISADVANTAGES OF PURPOSIVE SAMPLING:PURPOSIVE SAMPLING:

Potential for inaccuracy in the Potential for inaccuracy in the researcher’s criteria and resulting researcher’s criteria and resulting sample selection.sample selection.

A.A. Simple random samplingSimple random samplingB.B. Stratified random samplingStratified random samplingC.C. Cluster samplingCluster samplingD.D. Two-stage random samplingTwo-stage random samplingE.E. Convenience samplingConvenience samplingF.F. Purposive samplingPurposive samplingG.G. No sampling—entire population is being No sampling—entire population is being

studied.studied.

Identify Types of SamplingIdentify Types of Sampling

1._____ A researcher is interested in interviewing 1._____ A researcher is interested in interviewing a group of New York City police officers. She a group of New York City police officers. She goes to the main precinct in Manhattan and asks goes to the main precinct in Manhattan and asks for volunteers to be interviewed. The researcher for volunteers to be interviewed. The researcher then pays for the interviews.then pays for the interviews.

2._____ A researcher is interested in interviewing 2._____ A researcher is interested in interviewing all the members of the New York City police all the members of the New York City police force who do not live in the city. He gets a roster force who do not live in the city. He gets a roster of the names of all officers on the force, randomly of the names of all officers on the force, randomly selects five police stations, and then conducts selects five police stations, and then conducts interviews of all officers in those stations.interviews of all officers in those stations.

3._____ A researcher is interested in interviewing 3._____ A researcher is interested in interviewing alumni of San Simeon College who graduated alumni of San Simeon College who graduated between the years 1990 and 1996. He gets the roster between the years 1990 and 1996. He gets the roster of the names of these individuals from the alumni of the names of these individuals from the alumni office and mails a questionnaire to everyone on this office and mails a questionnaire to everyone on this roster.roster.

4._____ Another researcher is also interested in 4._____ Another researcher is also interested in interviewing alumni of San Simeon College who interviewing alumni of San Simeon College who graduated between the years 1990 and 1996. He gets graduated between the years 1990 and 1996. He gets the roster of the names of these individuals from the the roster of the names of these individuals from the alumni office, selects the names of 100 individuals alumni office, selects the names of 100 individuals who graduated during these years using a table of who graduated during these years using a table of random numbers, and then mails a questionnaire to random numbers, and then mails a questionnaire to everyone selected. everyone selected.

5._____ A researcher is interested in identifying the 5._____ A researcher is interested in identifying the attitudes of the physicians who work for Keyser attitudes of the physicians who work for Keyser Hospital toward the Republican plan for health care. Hospital toward the Republican plan for health care. She obtains a list of all the Keyser Medical Centers in She obtains a list of all the Keyser Medical Centers in Southern California and randomly selects ten of these Southern California and randomly selects ten of these Centers. Then she obtains a list of all the physicians Centers. Then she obtains a list of all the physicians at these Centers and randomly selects eight at these Centers and randomly selects eight physicians from each Center to interview.physicians from each Center to interview.

6._____ A graduate student enrolled in the Marriage 6._____ A graduate student enrolled in the Marriage and Family Counseling Program at Daytona and Family Counseling Program at Daytona University is interested in determining how other University is interested in determining how other graduate students feel about the program. He graduate students feel about the program. He interviews all of the students he has access to on a interviews all of the students he has access to on a given Monday night when he takes one of his given Monday night when he takes one of his counseling courses.counseling courses.

7._____ A student enrolled in the Hotel and 7._____ A student enrolled in the Hotel and Restaurant Management School at Colorado Restaurant Management School at Colorado State is researching the best restaurants in State is researching the best restaurants in Denver based on the opinions of food critics. Denver based on the opinions of food critics. She begins by asking her advisor who refers She begins by asking her advisor who refers the student to four food critics who have the student to four food critics who have written extensively on the subject and whom written extensively on the subject and whom the student then contacts to interview for her the student then contacts to interview for her study.study.

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