Presentation 070412

EDU 702 :Research MethodologySampling

Adibah Halilah bt Abdul Mutalib

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Topic areas:

Definition

• Population

• Sample

Identify & Contrast

• Target and Accessible population

• Random Sampling and Non-Random

Random Sampling

• Types of Random Sampling.

• How to select a random sample.

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Problem : Relationship

between stress levels and smoking among university

students

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Population of all university students in Malaysia = 12,000

Population of university students in UITM = 4,000

Population of male students = 1,400

10% Populations of UITM first year male students = 140

Research question : You would like to know the number of cigarettes the average university students smokes

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Definition of a Sample

• A small group of people studied to collect information to draw conclusion about the larger group

Sample

• Process of selecting the people (individuals) to be observed ( studied)Sampling

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Example of sample within a population

Sample:

information obtained

Population:

results of studies applied here

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700

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Questions: Can a Sample & Population have the same groups of people?

Smokers at University

All smokers

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Population – Smokers at University

Sample – Year 1 university students who are smokers

Discussion: How to select Sample?

Effects of eating “Nasi Lemak” for breakfast on young students.

Teachers view about teaching Math and Science in Bahasa Malaysia.

Students addiction to computer games and poor grades.

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How to define the population

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Stage 1: Define the population

• Who can you administer the results to?

• Any size

• Need to have at least one characteristic different from other population

Stage 2 : Identify “Who” or “What”

• Educator

• Object

TARGET vs. ACCESSIBLE POPULATION

• Ideal group/actual group researchers like to generalize

• Rarely availableTARGET

• Those who researchers are able to generalize

• Actual choiceACCESSIBLE

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Advantages of defining & narrowing population

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Money Time Effort

Random vs. Non-random-Sampling

Random Non-RandomSampling (Purposive)

All have equal and independent chance

Chosen based on a criteria

Selects a representative of population

No equal chance

Should be large and random Some have no chance at all

No bias Some types show biasness

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Random Sampling Methods

(A) Simple Random Sampling

(B) Stratified Random Sampling

(C) Cluster Random Sampling

(D) Two-stage Random Sampling

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(A) Simple Random Sampling ( 1 of 2)

• Each individual has equal and independent chance of selection

• The larger the sample, the more it represents the population

• Any differences is not due to biasness

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Simple Random Sampling (2 of 2)

• Method of finding individuals :

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Use a table of random numbers ( statistic book)

Choose any number on the

column

Read the numbers to select your

sample

Using the Table of Random Numbers

• Step 1: Select column of numbers

• Step 2: Choose any number on the column

• Step 3: Read the first 4 digits ( if you have population of 4 digits)

• Step 4: Pick out numbers and write them down.

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Exercise: Select the first 30 numbers for a population of 300.

Column 1 Column 2 Column 3 Column 4

099922 231100 182203 012030

122331 334444 092010 231102

644632 088765 001220 120301

162311 755664 005440 909201

234577 112344 194020 718291

344666 412346 230440 503813

092303 080902 210490 120311

009330 006102 530209 301020

230420 003233 409201 015663

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Answer:

• Looking at column 1:– Selected individuals are :

• 099

• 122

• 644

• 162

• 234

• 344

• 092

• 009

• 230

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(B) Stratified Random Sampling

• Certain ‘strata’ selected

• Sample in same proportion as they exist in the population

• Advantages: Increases likelihood of representativeness

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Calculating Stratified Random Sampling

• Step 1: Identify the target ( accessible) population

• Step 2: Select the ratio of their relationship

• Step 3: Determine the % of target population used as sample

• Step 4: Calculate the % sample for each strata

• Step 5: Use Table of random numbers to find the individuals in the respective strata

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Select gender individuals as they exist in the population ( 365)

Female

• 60 %

• 60 % of 365 = 219

Male

• 40%

• 40 % of 365 = 146

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Therefore, Female : Male 60 : 40219 : 146

Now, select 40 % of each strata as your representative…

Female : Male88 : 58

(C ) Cluster Random Sampling

• Ideal to include certain groups/ cluster

• However at times it is not possible to select individual due to

• Time

• Effort

• Select individuals based on ( not individuals)• Groups

• Clusters

• Subjects

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All Year 6 students in Selangor

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1

98

1110

1312

7

6

1

5

4

3

2

Selected schools chosen as clusters

Cluster random sampling…

Advantages

Disadvantages

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Common mistake made with Cluster random sampling.

• Randomly selecting only one cluster as a sample and choosing to interview/ survey all

• Cluster must be randomly selected not individuals

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(D) Two-stage Random Sampling

• Combination of Cluster random sampling and individual random sampling

– First select clusters randomly

– Then select students randomly from the clusters.

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FD

ABPO

KJ

XT

NH

RS

XT

PO

RS

P, T, S

Thank you…

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