The basic of educational research sampling

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. Each number from zero to the required number. Each individual must have the same number of digits as individual must have the same number of digits as each other individual.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 Go to the next number in the column and and repeat step #7 until the desired number repeat step #7 until the desired number of 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.

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

Less time-consumingLess time-consuming

NONRANDOM SAMPLING NONRANDOM SAMPLING METHODSMETHODS

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.

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.

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.

DISADVANTAGES OF DISADVANTAGES OF CONVENIENCE SAMPLING:CONVENIENCE SAMPLING:

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

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 “judgment” sampled. It is also called “judgment” sampling.sampling.

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.

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