RS 06 Sampling and Participants.ppt

8/12/2019 RS 06 Sampling and Participants.ppt

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Sampling and Participants

Dr. K. A. Korb

University of Jos


2/19

Outline

Population Validity

Sampling Methods

Simple Random Sampling

Stratified Sampling

Cluster Sampling

Convenience Sampling

Sample Size

Dr. K. A. Korb

University of Jos


3/19

Population Validity

Extent that an experiments results cangeneralize beyond participants in aparticular study to a larger group of

people Research Example: A descriptive study

examining the extent of parentsinvolvement in schools

Dr. K. A. Korb

University of Jos


4/19

Parents in these two samples (government school vs.Hillcrest) will likely have different involvement in theirchilds education because of many different reasons finances, parental education, trust of school officials, etc.

The purpose of sampling validity is to make a strongargument for why the results of your study will generalizebeyond those who participated in your study.

PopulationAll Nigerian parents with children in school

SampleAll Nigerian parents with students

in Government Secondary School

SampleAll Nigerian parents with studentsin Hillcrest

Dr. K. A. Korb

University of Jos


5/19

Simple Random Sampling

Definition: All individuals in the definedpopulation have an equal chance of beingpart of the sample.

Advantage: Conclusions from the datacan be generalized to the largerpopulation

Disadvantage: Difficult to implement, sovery few studies actually use simplerandom sampling

Dr. K. A. Korb

University of Jos


6/19

Simple Random Sampling Example

Population:All Nigerian parents with children in school

Size: Millions of adults

Sample:Those randomly chosen from the population.

Size: 100-200

Participants are chosen randomlyeither through a random numbertable or putting all names in a hat.

For this study, simple randomsampling would be practicallyimpossible.

Dr. K. A. Korb

University of Jos


7/19

Random Sampling vs.

Random Assignment

Random Sampling: Randomly selecting thosepeople who will participatein your study.

Allows you to generalize your findings beyond thesample of your study.

However, few educational studies can practically userandom selection.

Random Assignment: Once you participantshave been selected,they are randomly placed

into the treatment and control groups. Only applies to experimental design

MUSTbe used for an experiment to be a trueexperiment.

Dr. K. A. Korb

University of Jos


8/19

Random Sampling

Population

Sample

Randomly chose people from thepopulation to be part of theresearch sample.

Dr. K. A. Korb

University of Jos


9/19

Random Assignment

Sample1. Names of allparticipants areplaced in a hat

Treatment

Group

Control

Group

2. As names are drawn out of the

hat, they are placed in alternatingorder into the treatment andcontrol groups.

Dr. K. A. Korb

University of Jos


10/19

Stratified Sampling

Definition: Select a sample so certain subgroupscan be adequately represented Subgroups, or stratums,are identified by demographic

variables of interest to the study, such as gender,ethnicity, age, occupation, etc.

Random sampling will be used within each stratum.

Use If: The group is heterogeneous on an important variable

(e.g., ethnicity, gender).

or The purpose of the study is to compare groups of

different characteristics (e.g., a causal-comparativestudy)

Dr. K. A. Korb

University of Jos


11/19

Stratified Random Sampling Example

In the research example, one research questionmay compare the participation of mothers to theparticipation of fathers in their childs education. To test the difference between mothers and fathers, an

equal number of mothers and fathers must be selected

for the sample. Therefore, the population should first be divided into

male and female, and then random selection appliedwithin each group.

Procedure:1. Determine the stratumsto be sampled.2. Determine the number of participants necessary for

each stratum.3. Randomly sample participants from within each

sample.

Dr. K. A. Korb

University of Jos


12/19

Stratified Random Sampling Example

Population Stratum:Fathers of children in school

Sample

Randomly chose thesame number fromboth stratums.Population Stratum:

Mothers of children in school

The resulting sample will havean equal number ofparticipants from both

stratums.Dr. K. A. KorbUniversity of Jos


13/19

Cluster Sampling

Definition: Randomly sample a naturallyoccurring group of people

For example: A group could be a classroom of students

Advantage: Easier to conduct the study.

Disadvantage: Regular statistics CANNOT beconducted with cluster sampling. Instead of conducting statistics on participants data,

you have to conduct the statistics on the groups data.

Therefore, finding significant results is considerablymore difficult.

Dr. K. A. Korb

University of Jos


14/19

Cluster Sampling Example

Population Groups:Schools in Nigeria

Sample

Randomly chose thegroups from thepopulation.

The resulting sample will beanalyzed based on the GROUPdata.

Dr. K. A. Korb

University of Jos


15/19


Definition: Selects a sample that suits thepurpose of the study and is convenient.

Advantage: Practically, most of the othersampling methods are impossible to accomplish.A strategic convenience sample makespsychological and educational research possible.

Disadvantage: The researcher has to build acase in the conclusion of their paper about thegroup of people the studys findings willgeneralize to.

Note: Virtually all educational research usesconvenience sampling, perhaps with someelements of random sampling or stratifiedrandom sampling.

Dr. K. A. Korb

University of Jos


16/19


When using convenience sampling, youwill improve the quality of your work ifyou:

Specifically describe the characteristics of yoursample.

Give a rationale for why the sample wasappropriate for your study

Specify the population to which your resultswill likely generalize.

Dr. K. A. Korb

University of Jos

Dr K A Korb


17/19

Convenience Sampling Example

Population:All Nigerian parents with children in school

Sample

Participants are chosen from agroup that is convenient to theexperimenter and relevant for thepurposes of the study.

This convenience sample includes participants fromfour schools that are geographically close to theexperimenter and schools where the experimenterpersonally knows the headmaster. However, theexperimenter made a point to select two public andtwo private schools, as well as a school with mostlywealthy children, a school with mostly poor children,

and two schools in between because thesecharacteristics may influence the results of the study.

Dr. K. A. Korb

University of Jos


18/19

Sample Size

General Rule: Larger samples are better

Larger samples more accurately reflect thecharacteristics of the general population.

Larger samples also increase your chances ofgetting significant results for your studybecause one of the values that determinestatistical significance is the size of thesample.

Exception: Case studies and qualitativestudies tend to use smaller sample sizes

Dr. K. A. Korb

University of Jos


19/19

Minimum Sample Size

Descriptive Survey Research Designs At least 100 participants in each group

Causal-Comparative Research Designs

At least 15 participants in each group to becompared

Correlational Research Designs At least 30 participants

Experimental Research Designs At least 15 participants in the control group

and at least 15 participants in each treatmentgroup.

Dr. K. A. Korb

Uni ersit of Jos

Documents

RS 06 Sampling and Participants.ppt