Selection of Population and Sampling Technique

8/13/2019 Selection of Population and Sampling Technique

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SELECTION OF POPULATION AND

SAMPLING TECHNIQUE

The research generally prefers

a sample to a population frame

for a reason of:Economy of time

Effort

Cost


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POPULATION

Refers to the universe or the sum

total of all elements under

consideration. It is a larger group about which

your generalization is made.

Gay (1976) defines it as the groupto which a researcher would like

the results to be generalizable.


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SAMPLE

According to Ferguson (1976) any

sub-aggregate drawn from the

population, or it a portion of a

population.


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Kerlinger (1973) says, all members

of a well defined class of people,

events or objects, which is theactual statistical values and Its

characteristic are called

PARAMETERS


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Example of population frame;

All the TB patient with gastric ulcer inSan Lazaro Hospital.

All five-year-old children in the districtof Makati suffering from severe

diarrhea. All Nursing graduates of Perpetual

Help College Manila who passed the

board examination for the year 2012. Some population frame are either finite

or countable while others are infinitecan not be counted.


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Example of Finite Population

All patient with stomach ulcers in Makati medical

Center Patients who died of pneumonia in UST Hospital for

2000-2001.

All nurses who have gained employment abroad.

Sometimes what makes a population countable is that

it is delimited to a certain period of time or samplecan be derived. Ex. The number of nurses who passed

the

board exam is difficult to obtain, but it can be done,

hence population of all nurses who passed the boardexam is countable for a particular year desired. This

shows the importance of delimitation in the research.


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Example of Infinite Population

All cars that passed along Dapitan street All stars in the sky

All numbers of stone in the seashore.

Look at the examples of all cars that will pass

along Dapitan which can be counted, but

researcher who is very interested in the topic

may

decide to use a quota sample and take the first

100 or 200 cars that will pass along Dapitan

street.


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Factors Affecting in the

Selection of a Population

1. Objectives of the research

2. Availability of data

3. Nature of research

4. Variables to be measured, assessed

or associated

5.

Inferences to be made


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Some Minimum Acceptable

Sizes of Sample

Descriptive Research 10% of the

population for smaller population a

minimum of 20% may be required.

Correlational research 30 subjects

Ex post facto or casual comparative

research 15 subjects per group

Experimental research 15 subjects pergroup. Some authorities believes that 30

per group should be considered minimum.


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SAMPLING

A process which involves taking a part

of a population, making observation on

this representative group and thengeneralizing the findings to a bigger

population


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Slovin Formula to determine the

sample size of a population


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n = sample size

N = population sizee = the desired margin of error

Example:

Suppose the population has the size of 1000.what

size of the sample can be derived from it using a0.05

margin of error? Remember that the assumption of a normal

distribution of the population should beconsidered. When the normal approximation is

small or poor, this sample size formula does


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Sampling

Techniques/Strategies

The methods of deriving samples from

probability or nonprobability is called

sampling technique. There is therefore a

one-to-one correspondence between asample and a sampling technique or that

sample has its own unique sampling

technique.

There are two kinds of samples:

Probability sampletaken from one where

all elements in the population frame have

an equal chance of being selected.


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Nonprobabilityconsist of non-randomsample subjects. There is less chance ofobtaining a representative sample.

Different Types of Probability Samplesa. Random Samplinga method of selecting

sample size from a universe such that eachmembers of the population has an equal

chance of being selected as the sample. Thisstrategy is known as the best procedure.

Pre-requisite for Random Sampling:

1. Define the population

2. List all members of the population3. Select the sample by employing an adequate

procedure where every member has an equalchance.


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Two Basic Principles in Random Sampling

1. Equi-probabilitythis means that the member of

the population has an equal chances of being

included in the sample.

2. Independencerefers to the fact that when one

member is selected for the sampling this should

not affect the chances of the other members

getting choosen.

How it is being selected

1. Lottery Sampling or the fish bowl technique-this

procedure can be applied by first assigning

numbers to the participants of the populationassembling them in a sampling frame.

2. Table of Random Numbers-is the most systematic

technique for getting sample units at random.


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b. Systematic Sampling-it is a strategy for

selecting the members of the sample that

allows only chance and a system todetermine membership in the sample.

Systemis a planned strategy for selecting

members after a starting point to be

selected at random.

c. Stratified Random Sample-strategy for

selecting samples in such a way that

specific sub-groups (strata) will havesufficient number of representative within

the sample to provide ample numbers of

sub-analysis of the members of these sub-

groups.


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d. Cluster Sampling-results when population

is divided into group or cluster. A cluster

sampling technique, is a sampling

technique where groups and cluster not

individuals are selected. It is used when

large-scale survey is undertaken whileother sampling techniques are concerned

only with a few subjects or a few locations.

e. Multistage Sampling-is rarely used,

because of its complexity of its strategyand also it incurs a lot of effort, time and

expense.


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Nonprobability Sample

Convenience Sampling It is asampling strategy based on the

convenience of the researcher. For

instance if the researcher wants toknow about national reconciliation in

the Filipinos in the Philippines

through telephone interviews, he willhave the chance to interview only

those who have telephone to the bias

against those who have no

telephones. Such sampling is done for


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Purposive or deliberate sampling-if the

researcher is interested in finding out

for example, a particular reaction of

some students on the devaluation ofpeso, instead of asking the opinion of

all students in various colleges or

universities in Metro Manila, he maypurposely ask only the group leaders

of a particular college. This is sampling

with purpose.


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Selection of Population and Sampling Technique